feat: implement scoped join attempts and tickets (#10)

Closes #10

docs/api/rendezvous-v1.json

@@ -686,8 +686,28 @@
               }
             }
           },
-          "501": {
+          "400": {
-            "description": "Not Implemented",
+            "description": "Bad Request",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Not Found",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Service Unavailable",
             "content": {
               "application/json": {
                 "schema": {
@@ -726,8 +746,109 @@
               }
             }
           },
-          "501": {
+          "400": {
-            "description": "Not Implemented",
+            "description": "Bad Request",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Not Found",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "Conflict",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "429": {
+            "description": "Too Many Requests",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Service Unavailable",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
+    "/v1/join-attempts/{attemptId}": {
+      "delete": {
+        "tags": [
+          "Join attempts"
+        ],
+        "operationId": "CancelJoinAttempt",
+        "parameters": [
+          {
+            "name": "attemptId",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          },
+          {
+            "name": "X-Rendezvous-Client-Punch-Capability",
+            "in": "header",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          }
+        ],
+        "responses": {
+          "204": {
+            "description": "No Content"
+          },
+          "400": {
+            "description": "Bad Request",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Not Found",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Service Unavailable",
             "content": {
               "application/json": {
                 "schema": {

docs/architecture/0003-state-privacy-availability-and-budgets.md

@@ -64,7 +64,7 @@ them but must not raise them without security review.
 | Browser page | 100 listings and 256 KiB encoded response; opaque cursor; stable bounded sort |
 | UDP datagram accepted | 1,200 bytes; oversized or fragmented application payloads are dropped without response |
 | Opaque HTTP credential | 1,024 bytes encoded |
-| UDP capability or ticket | 768 bytes encoded, with the complete datagram still at most 1,200 bytes |
+| UDP capability or connection ticket | 192 base64url characters; NAT punch capabilities also remain below LiteNetLib's 256-character token ceiling; complete datagram at most 1,200 bytes |
 | Clock skew | 30 seconds maximum when validating issued/not-before/expiry times |
 | Lease lifetime | 60 seconds; renewal accepted from 30 seconds; no client-selected extension |
 | Host presence freshness | 20 seconds |

docs/architecture/0008-scoped-join-attempts-and-tickets.md

@@ -0,0 +1,66 @@
+# ADR 0008: scoped join attempts and one-time connection tickets
+
+- Status: Accepted
+- Date: 2026-07-16
+- Tracking: #10
+
+## Decision
+
+Join creation is an unauthenticated public operation because v1 does not treat a
+Rendezvous caller as game identity. The HTTP source address is normalized and
+converted to a process-keyed opaque subject for idempotency and bounded policy
+accounting; raw addresses and the derived subject are never returned or logged.
+A successful request means only that this network client may try to connect to
+this active session. It does not reserve capacity or grant gameplay admission.
+
+Creation validates the v1 contract, caller idempotency key, enabled tenant policy,
+exact gameplay protocol, listing scope, live lease, and fresh authenticated host
+presence in one atomic store operation. A listing advertised as full remains
+joinable because its player count is advisory and the game host owns the final
+capacity, identity, ban, and admission decision.
+
+Each attempt derives independent host-punch, client-punch, and connection-ticket
+credentials plus opaque attempt and mediation IDs from a process-ephemeral HMAC
+key, the client subject, the complete canonical request fingerprint, a fresh salt,
+and a purpose/role label. Credentials are 32-byte base64url values (43 characters),
+below both the 192-character Rendezvous capability ceiling and LiteNetLib's
+256-character NAT token ceiling. State retains keyed credential fingerprints,
+derivation inputs, and salt—not issued plaintext. All diagnostic string
+representations redact credentials and derivation material.
+
+The client receives only its punch capability. A host polls its own listing with
+the lease token in `X-Rendezvous-Lease-Token` and receives only host-role
+capabilities through a signed, listing-bound, five-minute cursor. Replaying an
+identical join request returns the same live attempt; changing the request under
+the same owner/key conflicts. A client may cancel with its punch capability in
+`X-Rendezvous-Client-Punch-Capability`; cancellation atomically removes the
+attempt. Listing deletion, expiry, revocation, or process restart removes every
+associated attempt and credential fingerprint.
+
+Endpoint binding remains role- and capability-specific. The first endpoint
+observed for a role wins atomically; an exact UDP duplicate is idempotent, while
+endpoint or role substitution is rejected. An introduction is consumable once
+only after both roles bind, so concurrent attempts for the same listing cannot
+cross-wire.
+
+The connection ticket is distinct from both punch capabilities and is reproduced
+only after introduction succeeds. Its window begins at that moment and lasts at
+most 20 seconds without outliving the 30-second attempt. The server has an atomic
+fingerprint-consumption seam for mediator tests and revocation. On the game host,
+the SDK's bounded `ConnectionTicketValidator` stores a process-keyed digest,
+accepts an exact ticket once under a lock, rejects altered/cross-attempt/expired/
+revoked/replayed tickets, and zeroes retained digests and key material on disposal.
+Issue #11 carries the ticket in the authenticated introduction; issue #12 wires
+authorization and consumption into the caller-owned LiteNetLib coordinator.
+
+## Consequences
+
+- A join attempt is transport authorization, never proof of player identity or a
+  game slot.
+- Network-address-derived subjects are process-local abuse/idempotency scopes,
+  not stable user identifiers; stronger authenticated player scopes require a
+  future game-owned identity contract.
+- Cancellation after a ticket has reached a host must also revoke that host's
+  local validator entry; coordinator wiring owns that race in issue #12.
+- Capability and ticket plaintext never enter browser results, state snapshots,
+  logs, metrics, or generated string representations.

docs/architecture/README.md

@@ -10,6 +10,7 @@ decision requires a superseding ADR and corresponding contract/test updates.
 - [ADR 0005: authenticated session lease and presence lifecycle](0005-session-lease-lifecycle.md)
 - [ADR 0006: bounded compatible session browser](0006-compatible-session-browser.md)
 - [ADR 0007: caller-owned .NET publisher and browser SDK](0007-caller-owned-dotnet-client-sdk.md)
+- [ADR 0008: scoped join attempts and one-time connection tickets](0008-scoped-join-attempts-and-tickets.md)
 - [Threat model](../security/threat-model.md)
 - [Security promise and test matrix](../security/control-matrix.md)
 - [Versioned HTTP and UDP contracts](../contracts/README.md)

docs/contracts/http-v1.md

@@ -33,6 +33,7 @@ the same value as a required query parameter.
 | `GET` | `/v1/sessions` | Browse compatible public sessions. |
 | `GET` | `/v1/sessions/{listingId}` | Resolve a public or explicitly shared unlisted listing. |
 | `POST` | `/v1/join-attempts` | Authorize and create a short-lived join attempt. |
+| `DELETE` | `/v1/join-attempts/{attemptId}` | Cancel an attempt using its client punch capability. |
 | `GET` | `/v1/sessions/{listingId}/join-attempts` | Let an authenticated host poll pending attempts. |
 | `POST` | `/v1/join-attempts/{attemptId}/outcome` | Report a bounded connection outcome. |
 | `GET` | `/health/live` | Report that the HTTP process is alive. |
@@ -49,6 +50,11 @@ for mutation operations are carried in their request bodies. Public browser
 responses contain no IP endpoints, lease tokens, punch capabilities, connection
 tickets, player identifiers, or gameplay state.
 
+Attempt cancellation sends the short-lived client punch capability in
+`X-Rendezvous-Client-Punch-Capability`. Join creation uses the observed HTTP
+source only for a process-keyed, short-lived idempotency/abuse scope; this is not
+player authentication and is never returned to callers.
+
 ## Idempotency, cursors, and retries
 
 Registration and join creation require a caller-generated visible-ASCII

src/FinalFactory.Rendezvous.Client/ConnectionTickets/ConnectionTicketValidator.cs

@@ -0,0 +1,232 @@
+using System.Security.Cryptography;
+using System.Text;
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Client;
+
+public enum ConnectionTicketConsumptionResult
+{
+    Accepted = 1,
+    NotFound = 2,
+    Expired = 3,
+    Rejected = 4,
+    AlreadyConsumed = 5,
+    Revoked = 6,
+}
+
+public sealed class ConnectionTicketValidator : IDisposable
+{
+    private readonly object _gate = new();
+    private readonly Dictionary<JoinAttemptId, TicketEntry> _tickets = [];
+    private readonly int _maximumAuthorizedTickets;
+    private readonly IConnectionTicketClock _clock;
+    private readonly byte[] _fingerprintKey = new byte[32];
+    private bool _disposed;
+
+    public ConnectionTicketValidator(int maximumAuthorizedTickets = 1_024)
+        : this(maximumAuthorizedTickets, new SystemConnectionTicketClock())
+    {
+    }
+
+    internal ConnectionTicketValidator(
+        int maximumAuthorizedTickets,
+        IConnectionTicketClock clock)
+    {
+        if (maximumAuthorizedTickets is < 1 or > 10_000)
+        {
+            throw new ArgumentOutOfRangeException(nameof(maximumAuthorizedTickets));
+        }
+
+        _maximumAuthorizedTickets = maximumAuthorizedTickets;
+        _clock = clock ?? throw new ArgumentNullException(nameof(clock));
+        RandomNumberGenerator.Fill(_fingerprintKey);
+    }
+
+    public bool TryAuthorize(
+        JoinAttemptId attemptId,
+        string connectionTicket,
+        DateTimeOffset expiresAt)
+    {
+        lock (_gate)
+        {
+            ThrowIfDisposed();
+            DateTimeOffset now = _clock.UtcNow;
+            if (attemptId.Value == Guid.Empty
+                || !ContractValidation.IsConnectionTicketValid(connectionTicket)
+                || expiresAt <= now)
+            {
+                return false;
+            }
+
+            RemoveExpired(now);
+            byte[] fingerprint = Fingerprint(connectionTicket);
+            if (_tickets.TryGetValue(attemptId, out TicketEntry? current))
+            {
+                bool idempotent = current.State == TicketState.Active
+                    && current.ExpiresAt == expiresAt
+                    && CryptographicOperations.FixedTimeEquals(current.Fingerprint, fingerprint);
+                CryptographicOperations.ZeroMemory(fingerprint);
+                return idempotent;
+            }
+
+            if (_tickets.Count >= _maximumAuthorizedTickets)
+            {
+                CryptographicOperations.ZeroMemory(fingerprint);
+                return false;
+            }
+
+            _tickets.Add(attemptId, new(fingerprint, expiresAt));
+            return true;
+        }
+    }
+
+    public ConnectionTicketConsumptionResult Consume(
+        JoinAttemptId attemptId,
+        string connectionTicket)
+    {
+        lock (_gate)
+        {
+            ThrowIfDisposed();
+            DateTimeOffset now = _clock.UtcNow;
+            if (attemptId.Value == Guid.Empty
+                || !ContractValidation.IsConnectionTicketValid(connectionTicket))
+            {
+                return ConnectionTicketConsumptionResult.Rejected;
+            }
+
+            if (!_tickets.TryGetValue(attemptId, out TicketEntry? entry))
+            {
+                RemoveExpired(now);
+                return ConnectionTicketConsumptionResult.NotFound;
+            }
+
+            if (entry.ExpiresAt <= now)
+            {
+                Remove(attemptId, entry);
+                return ConnectionTicketConsumptionResult.Expired;
+            }
+
+            if (entry.State == TicketState.Revoked)
+            {
+                return ConnectionTicketConsumptionResult.Revoked;
+            }
+
+            if (entry.State == TicketState.Consumed)
+            {
+                return ConnectionTicketConsumptionResult.AlreadyConsumed;
+            }
+
+            byte[] supplied = Fingerprint(connectionTicket);
+            bool matches = CryptographicOperations.FixedTimeEquals(entry.Fingerprint, supplied);
+            CryptographicOperations.ZeroMemory(supplied);
+            if (!matches)
+            {
+                return ConnectionTicketConsumptionResult.Rejected;
+            }
+
+            entry.State = TicketState.Consumed;
+            return ConnectionTicketConsumptionResult.Accepted;
+        }
+    }
+
+    public bool Revoke(JoinAttemptId attemptId)
+    {
+        lock (_gate)
+        {
+            ThrowIfDisposed();
+            RemoveExpired(_clock.UtcNow);
+            if (!_tickets.TryGetValue(attemptId, out TicketEntry? entry))
+            {
+                return false;
+            }
+
+            entry.State = TicketState.Revoked;
+            CryptographicOperations.ZeroMemory(entry.Fingerprint);
+            return true;
+        }
+    }
+
+    public void Dispose()
+    {
+        lock (_gate)
+        {
+            if (_disposed)
+            {
+                return;
+            }
+
+            foreach (TicketEntry entry in _tickets.Values)
+            {
+                CryptographicOperations.ZeroMemory(entry.Fingerprint);
+            }
+
+            _tickets.Clear();
+            CryptographicOperations.ZeroMemory(_fingerprintKey);
+            _disposed = true;
+        }
+    }
+
+    public override string ToString() => "[ConnectionTicketValidator: tickets and key redacted]";
+
+    private byte[] Fingerprint(string ticket)
+    {
+        byte[] encoded = Encoding.ASCII.GetBytes(ticket);
+        try
+        {
+            using HMACSHA256 hmac = new(_fingerprintKey);
+            return hmac.ComputeHash(encoded);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(encoded);
+        }
+    }
+
+    private void RemoveExpired(DateTimeOffset now)
+    {
+        foreach (KeyValuePair<JoinAttemptId, TicketEntry> item in _tickets
+                     .Where(item => item.Value.ExpiresAt <= now)
+                     .ToArray())
+        {
+            Remove(item.Key, item.Value);
+        }
+    }
+
+    private void Remove(JoinAttemptId attemptId, TicketEntry entry)
+    {
+        CryptographicOperations.ZeroMemory(entry.Fingerprint);
+        _tickets.Remove(attemptId);
+    }
+
+    private void ThrowIfDisposed()
+    {
+        if (_disposed)
+        {
+            throw new ObjectDisposedException(nameof(ConnectionTicketValidator));
+        }
+    }
+
+    private sealed class TicketEntry(byte[] fingerprint, DateTimeOffset expiresAt)
+    {
+        public byte[] Fingerprint { get; } = fingerprint;
+        public DateTimeOffset ExpiresAt { get; } = expiresAt;
+        public TicketState State { get; set; }
+    }
+
+    private enum TicketState
+    {
+        Active = 0,
+        Consumed = 1,
+        Revoked = 2,
+    }
+}
+
+internal interface IConnectionTicketClock
+{
+    DateTimeOffset UtcNow { get; }
+}
+
+internal sealed class SystemConnectionTicketClock : IConnectionTicketClock
+{
+    public DateTimeOffset UtcNow => DateTimeOffset.UtcNow;
+}

src/FinalFactory.Rendezvous.Client/Properties/AssemblyInfo.cs

@@ -0,0 +1,3 @@
+using System.Runtime.CompilerServices;
+
+[assembly: InternalsVisibleTo("FinalFactory.Rendezvous.Tests")]

src/FinalFactory.Rendezvous.Client/README.md

@@ -58,4 +58,22 @@ it when hosting stops. Use `IRendezvousPublisherClient` and
 `IRendezvousSessionBrowserClient` as injection seams in game tests. The SDK disposes
 the requests and responses it creates but never disposes the supplied `HttpClient`.
 
-See the repository's ADR 0007 for retry, paging, ownership, and failure semantics.
+The host-side `ConnectionTicketValidator` is a bounded, thread-safe one-time gate.
+Authorize only tickets delivered by the authenticated Rendezvous introduction,
+then consume the exact ticket presented by the direct LiteNetLib connection:
+
+```csharp
+using ConnectionTicketValidator tickets = new();
+tickets.TryAuthorize(attemptId, expectedTicket, expiresAt);
+ConnectionTicketConsumptionResult admission = tickets.Consume(
+    attemptId,
+    presentedTicket);
+```
+
+An `Accepted` ticket authorizes only this connection attempt. The game must still
+apply its own player identity, capacity, ban, and gameplay admission rules. Revoke
+the attempt on cancellation and dispose the validator during host shutdown so its
+keyed ticket digests are zeroed.
+
+See the repository's ADR 0007 for HTTP ownership/retry semantics and ADR 0008 for
+join-capability and connection-ticket security semantics.

src/FinalFactory.Rendezvous.Server/Browser/EphemeralCursorProtector.cs

@@ -0,0 +1,103 @@
+using System.Security.Cryptography;
+using System.Text;
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Server.Browser;
+
+internal sealed class EphemeralCursorProtector : IDisposable
+{
+    private readonly byte[] _key = RandomNumberGenerator.GetBytes(32);
+    private bool _disposed;
+
+    public string Protect(string prefix, ReadOnlySpan<byte> payload)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        string content = $"{prefix}.{EncodeBytes(payload)}";
+        byte[] signature = HMACSHA256.HashData(_key, Encoding.ASCII.GetBytes(content));
+        try
+        {
+            string cursor = $"{content}.{EncodeBytes(signature)}";
+            return ContractValidation.IsCursorValid(cursor)
+                ? cursor
+                : throw new InvalidOperationException("The protected cursor exceeds its contract limit.");
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(signature);
+        }
+    }
+
+    public bool TryUnprotect(string prefix, string? cursor, out byte[] payload)
+    {
+        payload = [];
+        if (_disposed || !ContractValidation.IsCursorValid(cursor))
+        {
+            return false;
+        }
+
+        string[] segments = cursor!.Split('.');
+        if (segments.Length != 3 || !string.Equals(segments[0], prefix, StringComparison.Ordinal))
+        {
+            return false;
+        }
+
+        byte[] expected = HMACSHA256.HashData(
+            _key,
+            Encoding.ASCII.GetBytes($"{segments[0]}.{segments[1]}"));
+        if (!TryDecodeBytes(segments[2], out byte[] supplied))
+        {
+            CryptographicOperations.ZeroMemory(expected);
+            return false;
+        }
+
+        bool validSignature = supplied.Length == expected.Length
+            && CryptographicOperations.FixedTimeEquals(supplied, expected);
+        CryptographicOperations.ZeroMemory(supplied);
+        CryptographicOperations.ZeroMemory(expected);
+        return validSignature && TryDecodeBytes(segments[1], out payload);
+    }
+
+    public void Dispose()
+    {
+        if (!_disposed)
+        {
+            _disposed = true;
+            CryptographicOperations.ZeroMemory(_key);
+        }
+    }
+
+    public override string ToString() => "[EphemeralCursorProtector: key redacted]";
+
+    private static string EncodeBytes(ReadOnlySpan<byte> bytes) => Convert
+        .ToBase64String(bytes)
+        .TrimEnd('=')
+        .Replace('+', '-')
+        .Replace('/', '_');
+
+    private static bool TryDecodeBytes(string value, out byte[] bytes)
+    {
+        bytes = [];
+        if (string.IsNullOrEmpty(value)
+            || value.Any(static character =>
+                character is not (>= 'A' and <= 'Z')
+                and not (>= 'a' and <= 'z')
+                and not (>= '0' and <= '9')
+                and not '-'
+                and not '_'))
+        {
+            return false;
+        }
+
+        string padded = value.Replace('-', '+').Replace('_', '/');
+        padded += (padded.Length % 4) switch { 0 => "", 2 => "==", 3 => "=", _ => "!" };
+        try
+        {
+            bytes = Convert.FromBase64String(padded);
+            return true;
+        }
+        catch (FormatException)
+        {
+            return false;
+        }
+    }
+}

src/FinalFactory.Rendezvous.Server/Browser/SessionBrowserCursorCodec.cs

@@ -1,5 +1,4 @@
 using System.Security.Cryptography;
-using System.Text;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using FinalFactory.Rendezvous.Contracts;
@@ -10,12 +9,10 @@ namespace FinalFactory.Rendezvous.Server.Browser;
 internal sealed class SessionBrowserCursorCodec : IDisposable
 {
     private const string Prefix = "rvc1";
-    private readonly byte[] _key = RandomNumberGenerator.GetBytes(32);
+    private readonly EphemeralCursorProtector _protector = new();
-    private bool _disposed;
 
     public string Encode(VisibleListingQuery query, SessionListingId after, DateTimeOffset now)
     {
-        ObjectDisposedException.ThrowIf(_disposed, this);
         BrowserCursorPayload payload = new()
         {
             GameId = query.Scope.GameId.Value,
@@ -26,19 +23,14 @@ internal sealed class SessionBrowserCursorCodec : IDisposable
             AfterListingId = after.ToString(),
             ExpiresAtUnixSeconds = now.AddMinutes(5).ToUnixTimeSeconds(),
         };
-        string encoded = EncodeBytes(JsonSerializer.SerializeToUtf8Bytes(payload, ContractJson.Options));
+        byte[] encoded = JsonSerializer.SerializeToUtf8Bytes(payload, ContractJson.Options);
-        string content = $"{Prefix}.{encoded}";
-        byte[] signature = HMACSHA256.HashData(_key, Encoding.ASCII.GetBytes(content));
         try
         {
-            string cursor = $"{content}.{EncodeBytes(signature)}";
+            return _protector.Protect(Prefix, encoded);
-            return ContractValidation.IsCursorValid(cursor)
-                ? cursor
-                : throw new InvalidOperationException("The browser cursor exceeds its contract limit.");
         }
         finally
         {
-            CryptographicOperations.ZeroMemory(signature);
+            CryptographicOperations.ZeroMemory(encoded);
         }
     }
 
@@ -57,31 +49,7 @@ internal sealed class SessionBrowserCursorCodec : IDisposable
             return true;
         }
 
-        if (_disposed || !ContractValidation.IsCursorValid(cursor))
+        if (!_protector.TryUnprotect(Prefix, cursor, out byte[] encodedPayload))
-        {
-            return false;
-        }
-
-        string[] segments = cursor.Split('.');
-        if (segments.Length != 3 || !string.Equals(segments[0], Prefix, StringComparison.Ordinal))
-        {
-            return false;
-        }
-
-        byte[] expected = HMACSHA256.HashData(
-            _key,
-            Encoding.ASCII.GetBytes($"{segments[0]}.{segments[1]}"));
-        if (!TryDecodeBytes(segments[2], out byte[] supplied))
-        {
-            CryptographicOperations.ZeroMemory(expected);
-            return false;
-        }
-
-        bool validSignature = supplied.Length == expected.Length
-            && CryptographicOperations.FixedTimeEquals(supplied, expected);
-        CryptographicOperations.ZeroMemory(supplied);
-        CryptographicOperations.ZeroMemory(expected);
-        if (!validSignature || !TryDecodeBytes(segments[1], out byte[] encodedPayload))
         {
             return false;
         }
@@ -118,64 +86,30 @@ internal sealed class SessionBrowserCursorCodec : IDisposable
         return true;
     }
 
-    public void Dispose()
+    public void Dispose() => _protector.Dispose();
-    {
-        if (!_disposed)
-        {
-            _disposed = true;
-            CryptographicOperations.ZeroMemory(_key);
-        }
-    }
 
     public override string ToString() => "[SessionBrowserCursorCodec: key and cursors redacted]";
-
-    private static string EncodeBytes(ReadOnlySpan<byte> bytes) => Convert
-        .ToBase64String(bytes)
-        .TrimEnd('=')
-        .Replace('+', '-')
-        .Replace('/', '_');
-
-    private static bool TryDecodeBytes(string value, out byte[] bytes)
-    {
-        bytes = [];
-        if (string.IsNullOrEmpty(value)
-            || value.Any(static character =>
-                character is not (>= 'A' and <= 'Z')
-                and not (>= 'a' and <= 'z')
-                and not (>= '0' and <= '9')
-                and not '-'
-                and not '_'))
-        {
-            return false;
-        }
-
-        string padded = value.Replace('-', '+').Replace('_', '/');
-        padded += (padded.Length % 4) switch { 0 => "", 2 => "==", 3 => "=", _ => "!" };
-        try
-        {
-            bytes = Convert.FromBase64String(padded);
-            return true;
-        }
-        catch (FormatException)
-        {
-            return false;
-        }
-    }
 }
 
 internal sealed class BrowserCursorPayload
 {
     [JsonRequired]
     public string GameId { get; set; } = string.Empty;
+
     [JsonRequired]
     public string EnvironmentId { get; set; } = string.Empty;
+
     [JsonRequired]
     public uint ProtocolVersion { get; set; }
+
     public string? RegionId { get; set; }
+
     [JsonRequired]
     public bool ExcludeFull { get; set; }
+
     [JsonRequired]
     public string AfterListingId { get; set; } = string.Empty;
+
     [JsonRequired]
     public long ExpiresAtUnixSeconds { get; set; }
 }

src/FinalFactory.Rendezvous.Server/Http/ContractEndpoints.cs

@@ -1,5 +1,7 @@
+using System.Net;
 using FinalFactory.Rendezvous.Contracts;
 using FinalFactory.Rendezvous.Server.Browser;
+using FinalFactory.Rendezvous.Server.JoinAttempts;
 using FinalFactory.Rendezvous.Server.Provisioning;
 using FinalFactory.Rendezvous.Server.Sessions;
 using FinalFactory.Rendezvous.Server.State;
@@ -67,7 +69,9 @@ internal static class ContractEndpoints
             .WithName("GetSession");
         sessions.MapGet("/{listingId}/join-attempts", BrowseHostJoinAttempts)
             .Produces<BrowseHostJoinAttemptsResponse>()
-            .Produces<ApiError>(NotImplementedStatus)
+            .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("BrowseHostJoinAttempts");
 
         RouteGroupBuilder attempts = endpoints
@@ -76,12 +80,22 @@ internal static class ContractEndpoints
         attempts.MapPost("/", CreateJoinAttempt)
             .Accepts<CreateJoinAttemptRequest>("application/json")
             .Produces<CreateJoinAttemptResponse>(StatusCodes.Status201Created)
-            .Produces<ApiError>(NotImplementedStatus)
+            .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status409Conflict)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
+            .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("CreateJoinAttempt");
+        attempts.MapDelete("/{attemptId}", CancelJoinAttempt)
+            .Produces(StatusCodes.Status204NoContent)
+            .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
+            .WithName("CancelJoinAttempt");
         attempts.MapPost("/{attemptId}/outcome", ReportConnectionOutcome)
             .Accepts<ReportConnectionOutcomeRequest>("application/json")
             .Produces<ReportConnectionOutcomeResponse>()
-            .Produces<ApiError>(NotImplementedStatus)
+            .Produces<ApiError>(StatusCodes.Status501NotImplemented)
             .WithName("ReportConnectionOutcome");
 
         return endpoints;
@@ -268,10 +282,55 @@ internal static class ContractEndpoints
         [FromQuery] int contractVersion,
         [FromHeader(Name = "X-Rendezvous-Lease-Token")] string leaseToken,
         [FromQuery] int? pageSize,
-        [FromQuery] string? cursor) => NotImplemented();
+        [FromQuery] string? cursor,
+        [FromServices] JoinAttemptService attempts,
+        CancellationToken cancellationToken)
+    {
+        JoinAttemptServiceResult<BrowseHostJoinAttemptsResponse> result = attempts.BrowseForHost(
+            listingId,
+            contractVersion,
+            leaseToken,
+            pageSize ?? ContractLimits.BrowserPageMaxItems,
+            cursor,
+            cancellationToken);
+        return result.Succeeded && result.Value is not null
+            ? Results.Ok(result.Value)
+            : Error(result.Error);
+    }
 
-    private static IResult CreateJoinAttempt([FromBody] CreateJoinAttemptRequest request) =>
+    private static IResult CreateJoinAttempt(
-        NotImplemented();
+        [FromBody] CreateJoinAttemptRequest request,
+        [FromServices] JoinAttemptService attempts,
+        HttpContext httpContext,
+        CancellationToken cancellationToken)
+    {
+        if (httpContext.Connection.RemoteIpAddress is not IPAddress remoteAddress)
+        {
+            return Error(RendezvousErrorCode.InvalidRequest);
+        }
+
+        string clientSubject = attempts.CreateAnonymousClientSubject(remoteAddress);
+        JoinAttemptServiceResult<CreateJoinAttemptResponse> result = attempts.Create(
+            clientSubject,
+            request,
+            cancellationToken);
+        return result.Succeeded && result.Value is not null
+            ? Results.Created($"/v1/join-attempts/{result.Value.AttemptId}", result.Value)
+            : Error(result.Error);
+    }
+
+    private static IResult CancelJoinAttempt(
+        JoinAttemptId attemptId,
+        [FromHeader(Name = "X-Rendezvous-Client-Punch-Capability")] string clientPunchCapability,
+        [FromServices] JoinAttemptService attempts,
+        CancellationToken cancellationToken)
+    {
+        JoinAttemptServiceResult<bool> result = attempts.Cancel(
+            attemptId,
+            clientPunchCapability,
+            cancellationToken);
+        return result.Succeeded ? Results.NoContent() : Error(result.Error);
+    }
 
     private static IResult ReportConnectionOutcome(
         JoinAttemptId attemptId,

src/FinalFactory.Rendezvous.Server/JoinAttempts/JoinAttemptCursorCodec.cs

@@ -0,0 +1,96 @@
+using System.Security.Cryptography;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Browser;
+
+namespace FinalFactory.Rendezvous.Server.JoinAttempts;
+
+internal sealed class JoinAttemptCursorCodec : IDisposable
+{
+    private const string Prefix = "rvj1";
+    private readonly EphemeralCursorProtector _protector = new();
+
+    public string Encode(
+        SessionListingId listingId,
+        JoinAttemptId after,
+        DateTimeOffset now)
+    {
+        JoinAttemptCursorPayload payload = new()
+        {
+            ListingId = listingId.ToString(),
+            AfterAttemptId = after.ToString(),
+            ExpiresAtUnixSeconds = now.AddMinutes(5).ToUnixTimeSeconds(),
+        };
+        byte[] encoded = JsonSerializer.SerializeToUtf8Bytes(payload, ContractJson.Options);
+        try
+        {
+            return _protector.Protect(Prefix, encoded);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(encoded);
+        }
+    }
+
+    public bool TryDecode(
+        string? cursor,
+        SessionListingId listingId,
+        DateTimeOffset now,
+        out JoinAttemptId? after)
+    {
+        after = null;
+        if (cursor is null)
+        {
+            return true;
+        }
+
+        if (!_protector.TryUnprotect(Prefix, cursor, out byte[] encodedPayload))
+        {
+            return false;
+        }
+
+        JoinAttemptCursorPayload? payload;
+        try
+        {
+            payload = JsonSerializer.Deserialize<JoinAttemptCursorPayload>(
+                encodedPayload,
+                ContractJson.Options);
+        }
+        catch (JsonException)
+        {
+            payload = null;
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(encodedPayload);
+        }
+
+        if (payload is null
+            || payload.ExpiresAtUnixSeconds <= now.ToUnixTimeSeconds()
+            || !string.Equals(payload.ListingId, listingId.ToString(), StringComparison.Ordinal)
+            || !JoinAttemptId.TryParse(payload.AfterAttemptId, out JoinAttemptId attemptId))
+        {
+            return false;
+        }
+
+        after = attemptId;
+        return true;
+    }
+
+    public void Dispose() => _protector.Dispose();
+
+    public override string ToString() => "[JoinAttemptCursorCodec: key and cursors redacted]";
+}
+
+internal sealed class JoinAttemptCursorPayload
+{
+    [JsonRequired]
+    public string ListingId { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public string AfterAttemptId { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public long ExpiresAtUnixSeconds { get; set; }
+}

src/FinalFactory.Rendezvous.Server/JoinAttempts/JoinAttemptService.cs

@@ -0,0 +1,327 @@
+using System.Net;
+using System.Security.Cryptography;
+using System.Text.Json;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Provisioning;
+using FinalFactory.Rendezvous.Server.Sessions;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Server.JoinAttempts;
+
+internal sealed record JoinAttemptServiceResult<T>(RendezvousErrorCode Error, T? Value = default)
+{
+    public bool Succeeded => Error == RendezvousErrorCode.None;
+}
+
+internal sealed record ConnectionTicketGrant(string Ticket, DateTimeOffset ExpiresAt)
+{
+    public override string ToString() => "[ConnectionTicketGrant: ticket redacted]";
+}
+
+internal sealed class JoinAttemptService(
+    GamePolicyRegistry policies,
+    IEphemeralRendezvousStore store,
+    ISessionCapabilityService capabilities,
+    JoinAttemptCursorCodec cursors,
+    IWallClock clock)
+{
+    public string CreateAnonymousClientSubject(IPAddress remoteAddress)
+    {
+        ArgumentNullException.ThrowIfNull(remoteAddress);
+        IPAddress normalized = remoteAddress.IsIPv4MappedToIPv6
+            ? remoteAddress.MapToIPv4()
+            : remoteAddress;
+        return capabilities.DeriveOpaqueIdentifier("join-http-client", normalized.ToString());
+    }
+
+    public JoinAttemptServiceResult<CreateJoinAttemptResponse> Create(
+        string clientSubject,
+        CreateJoinAttemptRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+        if (string.IsNullOrWhiteSpace(clientSubject))
+        {
+            throw new ArgumentException("A bounded client subject is required.", nameof(clientSubject));
+        }
+
+        RendezvousErrorCode validation = ValidateCreate(request);
+        if (validation != RendezvousErrorCode.None)
+        {
+            return new(validation);
+        }
+
+        if (!policies.TryGet(request.GameId, request.EnvironmentId, out GamePolicy? policy)
+            || policy is null)
+        {
+            return new(RendezvousErrorCode.NotFound);
+        }
+
+        if (!policy.AllowsProtocol(request.ProtocolVersion))
+        {
+            return new(RendezvousErrorCode.IncompatibleProtocol);
+        }
+
+        string requestFingerprint = ComputeRequestFingerprint(request);
+        string derivationSalt = capabilities.CreateDerivationSalt();
+        string hostCapability = Derive("join-host-punch", clientSubject, request, requestFingerprint, derivationSalt);
+        string clientCapability = Derive("join-client-punch", clientSubject, request, requestFingerprint, derivationSalt);
+        string connectionTicket = Derive("connection-ticket", clientSubject, request, requestFingerprint, derivationSalt);
+        if (!CredentialLengthsAreValid(hostCapability, clientCapability, connectionTicket)
+            || !capabilities.TryFingerprint(hostCapability, out SecretFingerprint hostFingerprint)
+            || !capabilities.TryFingerprint(clientCapability, out SecretFingerprint clientFingerprint)
+            || !capabilities.TryFingerprint(connectionTicket, out SecretFingerprint ticketFingerprint))
+        {
+            throw new InvalidOperationException("Derived join credentials violated their contract invariants.");
+        }
+
+        JoinAttemptId attemptId = new(capabilities.DeriveGuid(
+            "join-attempt-id",
+            clientSubject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            derivationSalt));
+        MediationHandle mediationHandle = new(capabilities.DeriveGuid(
+            "join-mediation-handle",
+            clientSubject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            derivationSalt));
+        StoreResult<StoredJoinAttempt> created = store.CreateJoinAttempt(new()
+        {
+            IdempotencyOwner = clientSubject,
+            IdempotencyKey = request.IdempotencyKey,
+            RequestFingerprint = requestFingerprint,
+            ClientSubject = clientSubject,
+            AttemptId = attemptId,
+            MediationHandle = mediationHandle,
+            Scope = new(request.GameId, request.EnvironmentId),
+            ListingId = request.ListingId,
+            ProtocolVersion = request.ProtocolVersion,
+            HostCapabilityFingerprint = hostFingerprint,
+            ClientCapabilityFingerprint = clientFingerprint,
+            ConnectionTicketFingerprint = ticketFingerprint,
+            CapabilityDerivationSalt = derivationSalt,
+            ScopeAttemptLimit = policy.MaxActiveJoinAttempts,
+        }, cancellationToken);
+        if (!created.Succeeded || created.Value is null)
+        {
+            return new(created.Code.ToContractError());
+        }
+
+        StoredJoinAttempt persisted = created.Value;
+        clientCapability = Derive(
+            "join-client-punch",
+            persisted.ClientSubject,
+            persisted.IdempotencyKey,
+            persisted.RequestFingerprint,
+            persisted.CapabilityDerivationSalt);
+        if (!capabilities.TryFingerprint(clientCapability, out SecretFingerprint persistedFingerprint)
+            || persistedFingerprint != persisted.ClientCapabilityFingerprint)
+        {
+            throw new InvalidOperationException("Stored join state could not reproduce its client capability.");
+        }
+        return new(RendezvousErrorCode.None, new CreateJoinAttemptResponse
+        {
+            AttemptId = persisted.AttemptId,
+            MediationHandle = persisted.MediationHandle,
+            ClientPunchCapability = clientCapability,
+            ExpiresAt = persisted.ExpiresAt,
+        });
+    }
+
+    public JoinAttemptServiceResult<BrowseHostJoinAttemptsResponse> BrowseForHost(
+        SessionListingId listingId,
+        int contractVersion,
+        string? leaseToken,
+        int pageSize,
+        string? cursor,
+        CancellationToken cancellationToken = default)
+    {
+        RendezvousErrorCode version = ContractValidation.ValidateContractVersion(contractVersion);
+        if (version != RendezvousErrorCode.None)
+        {
+            return new(version);
+        }
+
+        if (!ContractValidation.IsOpaqueHttpCredentialValid(leaseToken)
+            || !ContractValidation.IsPageSizeValid(pageSize)
+            || !ContractValidation.IsCursorValid(cursor)
+            || !capabilities.TryFingerprint(leaseToken, out SecretFingerprint leaseFingerprint))
+        {
+            return new(RendezvousErrorCode.InvalidRequest);
+        }
+
+        if (!cursors.TryDecode(cursor, listingId, clock.UtcNow, out JoinAttemptId? after))
+        {
+            return new(RendezvousErrorCode.InvalidRequest);
+        }
+
+        StoreResult<IReadOnlyList<StoredJoinAttempt>> found = store.BrowseHostJoinAttempts(new(
+            listingId,
+            leaseFingerprint,
+            pageSize + 1,
+            after), cancellationToken);
+        if (!found.Succeeded || found.Value is null)
+        {
+            return new(found.Code.ToContractError());
+        }
+
+        bool hasMore = found.Value.Count > pageSize;
+        StoredJoinAttempt[] page = found.Value.Take(pageSize).ToArray();
+        BrowseHostJoinAttemptsResponse response = new()
+        {
+            Items = page.Select(CreateHostAttempt).ToList(),
+            NextCursor = hasMore && page.Length > 0
+                ? cursors.Encode(listingId, page[^1].AttemptId, clock.UtcNow)
+                : null,
+        };
+        int encodedBytes = JsonSerializer.SerializeToUtf8Bytes(response, ContractJson.Options).Length;
+        return ContractValidation.IsBrowserResponseSizeValid(encodedBytes)
+            ? new(RendezvousErrorCode.None, response)
+            : new(RendezvousErrorCode.CapacityExceeded);
+    }
+
+    public JoinAttemptServiceResult<bool> Cancel(
+        JoinAttemptId attemptId,
+        string? clientPunchCapability,
+        CancellationToken cancellationToken = default)
+    {
+        if (!ContractValidation.IsCapabilityValid(clientPunchCapability)
+            || !capabilities.TryFingerprint(clientPunchCapability, out SecretFingerprint fingerprint))
+        {
+            return new(RendezvousErrorCode.InvalidRequest);
+        }
+
+        StoreResult<bool> cancelled = store.CancelJoinAttempt(new(attemptId, fingerprint), cancellationToken);
+        return cancelled.Succeeded
+            ? new(RendezvousErrorCode.None, true)
+            : new(cancelled.Code.ToContractError());
+    }
+
+    public JoinAttemptServiceResult<ConnectionTicketGrant> IssueConnectionTicket(
+        StoredJoinAttempt attempt)
+    {
+        ArgumentNullException.ThrowIfNull(attempt);
+        if (!attempt.IntroductionConsumed)
+        {
+            return new(RendezvousErrorCode.Conflict);
+        }
+
+        if (attempt.ConnectionTicketExpiresAt <= clock.UtcNow)
+        {
+            return new(RendezvousErrorCode.Expired);
+        }
+
+        string ticket = Derive(
+            "connection-ticket",
+            attempt.ClientSubject,
+            attempt.IdempotencyKey,
+            attempt.RequestFingerprint,
+            attempt.CapabilityDerivationSalt);
+        if (!ContractValidation.IsConnectionTicketValid(ticket)
+            || !capabilities.TryFingerprint(ticket, out SecretFingerprint fingerprint)
+            || fingerprint != attempt.ConnectionTicketFingerprint)
+        {
+            throw new InvalidOperationException("Stored join state could not reproduce its connection ticket.");
+        }
+
+        return new(RendezvousErrorCode.None, new(ticket, attempt.ConnectionTicketExpiresAt));
+    }
+
+    private HostJoinAttempt CreateHostAttempt(StoredJoinAttempt attempt)
+    {
+        string capability = Derive(
+            "join-host-punch",
+            attempt.ClientSubject,
+            attempt.IdempotencyKey,
+            attempt.RequestFingerprint,
+            attempt.CapabilityDerivationSalt);
+        if (!ContractValidation.IsCapabilityValid(capability)
+            || !capabilities.TryFingerprint(capability, out SecretFingerprint fingerprint)
+            || fingerprint != attempt.HostCapabilityFingerprint)
+        {
+            throw new InvalidOperationException("Stored join state could not reproduce its host capability.");
+        }
+
+        return new()
+        {
+            AttemptId = attempt.AttemptId,
+            MediationHandle = attempt.MediationHandle,
+            HostPunchCapability = capability,
+            ExpiresAt = attempt.ExpiresAt,
+        };
+    }
+
+    private static RendezvousErrorCode ValidateCreate(CreateJoinAttemptRequest request)
+    {
+        RendezvousErrorCode version = ContractValidation.ValidateContractVersion(request.ContractVersion);
+        if (version != RendezvousErrorCode.None)
+        {
+            return version;
+        }
+
+        return !ContractValidation.IsIdempotencyKeyValid(request.IdempotencyKey)
+            || string.IsNullOrEmpty(request.GameId.Value)
+            || string.IsNullOrEmpty(request.EnvironmentId.Value)
+            || request.ListingId.Value == Guid.Empty
+            || request.ProtocolVersion == 0
+            ? RendezvousErrorCode.InvalidRequest
+            : RendezvousErrorCode.None;
+    }
+
+    private static string ComputeRequestFingerprint(CreateJoinAttemptRequest request)
+    {
+        byte[] encoded = JsonSerializer.SerializeToUtf8Bytes(request, ContractJson.Options);
+        byte[] digest = SHA256.HashData(encoded);
+        CryptographicOperations.ZeroMemory(encoded);
+        try
+        {
+            return Encode(digest);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(digest);
+        }
+    }
+
+    private string Derive(
+        string purpose,
+        string clientSubject,
+        CreateJoinAttemptRequest request,
+        string requestFingerprint,
+        string derivationSalt) => Derive(
+            purpose,
+            clientSubject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            derivationSalt);
+
+    private string Derive(
+        string purpose,
+        string clientSubject,
+        string idempotencyKey,
+        string requestFingerprint,
+        string derivationSalt) => capabilities.DeriveCapability(
+            purpose,
+            clientSubject,
+            idempotencyKey,
+            requestFingerprint,
+            derivationSalt);
+
+    private static bool CredentialLengthsAreValid(
+        string hostCapability,
+        string clientCapability,
+        string ticket) =>
+        ContractValidation.IsCapabilityValid(hostCapability)
+        && ContractValidation.IsCapabilityValid(clientCapability)
+        && ContractValidation.IsConnectionTicketValid(ticket)
+        && hostCapability.Length <= ContractLimits.LiteNetLibNatTokenMaxCharacters
+        && clientCapability.Length <= ContractLimits.LiteNetLibNatTokenMaxCharacters;
+
+    private static string Encode(ReadOnlySpan<byte> bytes) => Convert
+        .ToBase64String(bytes)
+        .TrimEnd('=')
+        .Replace('+', '-')
+        .Replace('/', '_');
+}

src/FinalFactory.Rendezvous.Server/Program.cs

@@ -2,6 +2,7 @@ using System.Net;
 using FinalFactory.Rendezvous.Contracts;
 using FinalFactory.Rendezvous.Server.Browser;
 using FinalFactory.Rendezvous.Server.Http;
+using FinalFactory.Rendezvous.Server.JoinAttempts;
 using FinalFactory.Rendezvous.Server.Provisioning;
 using FinalFactory.Rendezvous.Server.Sessions;
 using FinalFactory.Rendezvous.Server.State;
@@ -122,6 +123,8 @@ else
     builder.Services.AddSingleton<SessionLeaseService>();
     builder.Services.AddSingleton<SessionBrowserCursorCodec>();
     builder.Services.AddSingleton<SessionBrowserService>();
+    builder.Services.AddSingleton<JoinAttemptCursorCodec>();
+    builder.Services.AddSingleton<JoinAttemptService>();
     builder.Services.AddSingleton(new ProvisioningReadiness(true));
 }
 

src/FinalFactory.Rendezvous.Server/Provisioning/PrincipalCredentialService.cs

@@ -122,7 +122,7 @@ internal sealed class PrincipalCredentialService
 
         if (!Base64Url.TryDecode(segments[3], out byte[]? suppliedSignature))
         {
-            return CredentialValidationResult.Invalid(CredentialValidationError.Malformed);
+            return CredentialValidationResult.Invalid(CredentialValidationError.SignatureInvalid);
         }
 
         string signedContent = $"{segments[0]}.{segments[1]}.{segments[2]}";
@@ -441,7 +441,14 @@ internal static class Base64Url
         try
         {
             bytes = Convert.FromBase64String(padded);
-            return true;
+            if (string.Equals(Encode(bytes), value, StringComparison.Ordinal))
+            {
+                return true;
+            }
+
+            CryptographicOperations.ZeroMemory(bytes);
+            bytes = [];
+            return false;
         }
         catch (FormatException)
         {

src/FinalFactory.Rendezvous.Server/Sessions/EphemeralCapabilityIssuer.cs

@@ -20,6 +20,7 @@ internal interface ISessionCapabilityService
         string idempotencyKey,
         string requestFingerprint,
         string derivationSalt);
+    string DeriveOpaqueIdentifier(string purpose, string value);
     bool TryFingerprint(string? capability, out SecretFingerprint fingerprint);
 }
 
@@ -91,6 +92,19 @@ internal sealed class EphemeralCapabilityIssuer : ISessionCapabilityService, IDi
         }
     }
 
+    public string DeriveOpaqueIdentifier(string purpose, string value)
+    {
+        byte[] digest = Derive(purpose, value);
+        try
+        {
+            return Encode(digest);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(digest);
+        }
+    }
+
     public bool TryFingerprint(string? capability, out SecretFingerprint fingerprint)
     {
         fingerprint = default;

src/FinalFactory.Rendezvous.Server/Sessions/SessionLeaseService.cs

@@ -127,7 +127,7 @@ internal sealed class SessionLeaseService(
             ownerLimit), cancellationToken);
         if (!created.Succeeded || created.Value is null)
         {
-            return new(MapStore(created.Code));
+            return new(created.Code.ToContractError());
         }
 
         ListingDefinition persisted = created.Value.Definition;
@@ -205,7 +205,7 @@ internal sealed class SessionLeaseService(
                 ExpiresAt = renewed.Value.LeaseExpiresAt,
                 RenewAfterSeconds = timing.LeaseRenewAfterSeconds,
             })
-            : new(MapStore(renewed.Code));
+            : new(renewed.Code.ToContractError());
     }
 
     public SessionServiceResult<bool> Update(
@@ -253,7 +253,7 @@ internal sealed class SessionLeaseService(
             request.Metadata), cancellationToken);
         return updated.Succeeded
             ? new(RendezvousErrorCode.None, true)
-            : new(MapStore(updated.Code));
+            : new(updated.Code.ToContractError());
     }
 
     public SessionServiceResult<bool> Delete(
@@ -291,7 +291,7 @@ internal sealed class SessionLeaseService(
             publisher.Subject), cancellationToken);
         return deleted.Succeeded || deleted.Code == StoreResultCode.NotFound
             ? new(RendezvousErrorCode.None, true)
-            : new(MapStore(deleted.Code));
+            : new(deleted.Code.ToContractError());
     }
 
     private RendezvousErrorCode GetAuthorizedListing(
@@ -315,7 +315,7 @@ internal sealed class SessionLeaseService(
         StoreResult<StoredListing> found = store.GetListing(listingId, false, cancellationToken);
         if (!found.Succeeded || found.Value is null)
         {
-            return MapStore(found.Code);
+            return found.Code.ToContractError();
         }
 
         if (!string.Equals(found.Value.Definition.OwnerSubject, publisher.Subject, StringComparison.Ordinal)
@@ -403,18 +403,6 @@ internal sealed class SessionLeaseService(
         _ => RendezvousErrorCode.Forbidden,
     };
 
-    private static RendezvousErrorCode MapStore(StoreResultCode code) => code switch
-    {
-        StoreResultCode.NotFound => RendezvousErrorCode.NotFound,
-        StoreResultCode.Expired => RendezvousErrorCode.Expired,
-        StoreResultCode.Revoked => RendezvousErrorCode.Forbidden,
-        StoreResultCode.Conflict => RendezvousErrorCode.Conflict,
-        StoreResultCode.CapacityExceeded => RendezvousErrorCode.CapacityExceeded,
-        StoreResultCode.ReplayRejected => RendezvousErrorCode.ReplayRejected,
-        StoreResultCode.Draining or StoreResultCode.ServiceUnavailable => RendezvousErrorCode.ServiceUnavailable,
-        _ => RendezvousErrorCode.InternalError,
-    };
-
     private static string ComputeRegistrationFingerprint(RegisterSessionRequest request)
     {
         RegisterSessionRequest canonical = new()

src/FinalFactory.Rendezvous.Server/State/EphemeralStateContracts.cs

@@ -35,6 +35,7 @@ internal sealed record EphemeralStoreOptions
     public TimeSpan LeaseLifetime { get; init; } = TimeSpan.FromSeconds(60);
     public TimeSpan PresenceLifetime { get; init; } = TimeSpan.FromSeconds(20);
     public TimeSpan JoinAttemptLifetime { get; init; } = TimeSpan.FromSeconds(30);
+    public TimeSpan ConnectionTicketLifetime { get; init; } = TimeSpan.FromSeconds(20);
     public TimeSpan ReplayLifetime { get; init; } = TimeSpan.FromSeconds(30);
     public TimeSpan IdempotencyLifetime { get; init; } = TimeSpan.FromMinutes(2);
     public TimeSpan GracefulDrainLifetime { get; init; } = TimeSpan.FromSeconds(30);
@@ -50,9 +51,17 @@ internal sealed record EphemeralStoreOptions
         RequireDuration(LeaseLifetime, TimeSpan.FromSeconds(60), nameof(LeaseLifetime));
         RequireDuration(PresenceLifetime, TimeSpan.FromSeconds(20), nameof(PresenceLifetime));
         RequireDuration(JoinAttemptLifetime, TimeSpan.FromSeconds(30), nameof(JoinAttemptLifetime));
+        RequireDuration(ConnectionTicketLifetime, TimeSpan.FromSeconds(20), nameof(ConnectionTicketLifetime));
         RequireDuration(ReplayLifetime, TimeSpan.FromSeconds(30), nameof(ReplayLifetime));
         RequireDuration(IdempotencyLifetime, TimeSpan.FromMinutes(10), nameof(IdempotencyLifetime));
         RequireDuration(GracefulDrainLifetime, TimeSpan.FromSeconds(30), nameof(GracefulDrainLifetime));
+        if (ConnectionTicketLifetime > JoinAttemptLifetime)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(ConnectionTicketLifetime),
+                "Connection tickets cannot outlive their join attempt.");
+        }
+
         if (IdempotencyLifetime < LeaseLifetime || IdempotencyLifetime < JoinAttemptLifetime)
         {
             throw new ArgumentOutOfRangeException(
@@ -246,7 +255,11 @@ internal sealed record CreateJoinAttemptCommand
     public required uint ProtocolVersion { get; init; }
     public required SecretFingerprint HostCapabilityFingerprint { get; init; }
     public required SecretFingerprint ClientCapabilityFingerprint { get; init; }
+    public required SecretFingerprint ConnectionTicketFingerprint { get; init; }
+    public required string CapabilityDerivationSalt { get; init; }
     public int ScopeAttemptLimit { get; init; } = int.MaxValue;
+
+    public override string ToString() => "[CreateJoinAttemptCommand: credentials redacted]";
 }
 
 internal sealed record AttemptEndpointBinding(
@@ -261,12 +274,28 @@ internal sealed record StoredJoinAttempt
     public required SessionListingId ListingId { get; init; }
     public required string ClientSubject { get; init; }
     public required uint ProtocolVersion { get; init; }
+    public required string IdempotencyKey { get; init; }
+    public required string RequestFingerprint { get; init; }
+    public required string CapabilityDerivationSalt { get; init; }
+    public required SecretFingerprint HostCapabilityFingerprint { get; init; }
+    public required SecretFingerprint ClientCapabilityFingerprint { get; init; }
+    public required SecretFingerprint ConnectionTicketFingerprint { get; init; }
     public required DateTimeOffset ExpiresAt { get; init; }
+    public required DateTimeOffset ConnectionTicketExpiresAt { get; init; }
     public AttemptEndpointBinding? HostEndpoint { get; init; }
     public AttemptEndpointBinding? ClientEndpoint { get; init; }
     public required bool IntroductionConsumed { get; init; }
+    public required bool ConnectionTicketConsumed { get; init; }
+
+    public override string ToString() => $"[StoredJoinAttempt {AttemptId}; credentials redacted]";
 }
 
+internal sealed record HostJoinAttemptQuery(
+    SessionListingId ListingId,
+    SecretFingerprint LeaseFingerprint,
+    int MaximumResults,
+    JoinAttemptId? AfterAttemptId = null);
+
 internal sealed record BindAttemptEndpointCommand(
     MediationHandle Handle,
     AttemptPeerRole Role,
@@ -275,9 +304,20 @@ internal sealed record BindAttemptEndpointCommand(
     ObservedEndpoint? LocalEndpoint);
 
 internal sealed record IntroductionEndpoints(
-    JoinAttemptId AttemptId,
+    StoredJoinAttempt Attempt,
     AttemptEndpointBinding Host,
-    AttemptEndpointBinding Client);
+    AttemptEndpointBinding Client)
+{
+    public JoinAttemptId AttemptId => Attempt.AttemptId;
+}
+
+internal sealed record CancelJoinAttemptCommand(
+    JoinAttemptId AttemptId,
+    SecretFingerprint ClientCapabilityFingerprint);
+
+internal sealed record ConsumeConnectionTicketCommand(
+    JoinAttemptId AttemptId,
+    SecretFingerprint ConnectionTicketFingerprint);
 
 internal sealed record ReplayConsumption(
     string Namespace,
@@ -316,8 +356,11 @@ internal interface IEphemeralRendezvousStore
     StoreResult<IReadOnlyList<StoredListing>> BrowseVisibleListings(VisibleListingQuery query, CancellationToken cancellationToken = default);
     StoreResult<StoredListing> BindHostPresence(BindHostPresenceCommand command, CancellationToken cancellationToken = default);
     StoreResult<StoredJoinAttempt> CreateJoinAttempt(CreateJoinAttemptCommand command, CancellationToken cancellationToken = default);
+    StoreResult<IReadOnlyList<StoredJoinAttempt>> BrowseHostJoinAttempts(HostJoinAttemptQuery query, CancellationToken cancellationToken = default);
+    StoreResult<bool> CancelJoinAttempt(CancelJoinAttemptCommand command, CancellationToken cancellationToken = default);
     StoreResult<StoredJoinAttempt> BindAttemptEndpoint(BindAttemptEndpointCommand command, CancellationToken cancellationToken = default);
     StoreResult<IntroductionEndpoints> ConsumeIntroduction(MediationHandle handle, CancellationToken cancellationToken = default);
+    StoreResult<bool> ConsumeConnectionTicket(ConsumeConnectionTicketCommand command, CancellationToken cancellationToken = default);
     StoreResult<bool> ConsumeReplay(ReplayConsumption consumption, CancellationToken cancellationToken = default);
     StoreResult<bool> RevokeListing(SessionListingId listingId, CancellationToken cancellationToken = default);
     StoreResult<int> RevokePrincipal(string subject, TimeSpan lifetime, CancellationToken cancellationToken = default);

src/FinalFactory.Rendezvous.Server/State/InMemoryEphemeralRendezvousStore.cs

@@ -390,6 +390,66 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
         return new(StoreResultCode.Success, Snapshot(attempt));
     }, cancellationToken);
 
+    public StoreResult<IReadOnlyList<StoredJoinAttempt>> BrowseHostJoinAttempts(
+        HostJoinAttemptQuery query,
+        CancellationToken cancellationToken = default) => Atomic<IReadOnlyList<StoredJoinAttempt>>(_ =>
+    {
+        ArgumentNullException.ThrowIfNull(query);
+        if (query.ListingId.Value == Guid.Empty
+            || !query.LeaseFingerprint.IsValid
+            || query.MaximumResults is < 1 or > ContractLimits.BrowserPageMaxItems + 1)
+        {
+            throw new ArgumentException("Host attempt query invariants are invalid.", nameof(query));
+        }
+
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (!_listings.TryGetValue(query.ListingId, out ListingEntry? listing)
+            || listing.Definition.LeaseFingerprint != query.LeaseFingerprint)
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        IReadOnlyList<StoredJoinAttempt> attempts = _attempts.Values
+            .Where(entry => entry.Command.ListingId == query.ListingId
+                && !entry.IntroductionConsumed
+                && (!query.AfterAttemptId.HasValue
+                    || entry.Command.AttemptId.Value.CompareTo(query.AfterAttemptId.Value.Value) > 0))
+            .OrderBy(static entry => entry.Command.AttemptId.Value)
+            .Take(query.MaximumResults)
+            .Select(Snapshot)
+            .ToArray();
+        return new(StoreResultCode.Success, attempts);
+    }, cancellationToken);
+
+    public StoreResult<bool> CancelJoinAttempt(
+        CancelJoinAttemptCommand command,
+        CancellationToken cancellationToken = default) => Atomic<bool>(_ =>
+    {
+        ArgumentNullException.ThrowIfNull(command);
+        if (command.AttemptId.Value == Guid.Empty || !command.ClientCapabilityFingerprint.IsValid)
+        {
+            throw new ArgumentException("Join cancellation invariants are invalid.", nameof(command));
+        }
+
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (!_attempts.TryGetValue(command.AttemptId, out AttemptEntry? attempt)
+            || attempt.ClientCapabilityFingerprint != command.ClientCapabilityFingerprint)
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        RemoveAttempt(command.AttemptId);
+        return new(StoreResultCode.Success, true);
+    }, cancellationToken);
+
     public StoreResult<StoredJoinAttempt> BindAttemptEndpoint(
         BindAttemptEndpointCommand command,
         CancellationToken cancellationToken = default) => Atomic<StoredJoinAttempt>(_ =>
@@ -447,7 +507,7 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
 
     public StoreResult<IntroductionEndpoints> ConsumeIntroduction(
         MediationHandle handle,
-        CancellationToken cancellationToken = default) => Atomic<IntroductionEndpoints>(_ =>
+        CancellationToken cancellationToken = default) => Atomic<IntroductionEndpoints>(now =>
     {
         if (!_available)
         {
@@ -471,12 +531,57 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
         }
 
         attempt.IntroductionConsumed = true;
+        TimeSpan ticketLifetime = TimeSpan.FromTicks(Math.Min(
+            _options.ConnectionTicketLifetime.Ticks,
+            (attempt.Deadline - now).Ticks));
+        attempt.TicketDeadline = now + ticketLifetime;
+        attempt.TicketWallExpiresAt = WallDeadline(now, ticketLifetime);
         return new(StoreResultCode.Success, new(
-            attempt.Command.AttemptId,
+            Snapshot(attempt),
             attempt.HostEndpoint,
             attempt.ClientEndpoint));
     }, cancellationToken);
 
+    public StoreResult<bool> ConsumeConnectionTicket(
+        ConsumeConnectionTicketCommand command,
+        CancellationToken cancellationToken = default) => Atomic<bool>(now =>
+    {
+        ArgumentNullException.ThrowIfNull(command);
+        if (command.AttemptId.Value == Guid.Empty || !command.ConnectionTicketFingerprint.IsValid)
+        {
+            throw new ArgumentException("Connection ticket invariants are invalid.", nameof(command));
+        }
+
+        if (!_available)
+        {
+            return new(StoreResultCode.ServiceUnavailable);
+        }
+
+        if (!_attempts.TryGetValue(command.AttemptId, out AttemptEntry? attempt)
+            || attempt.ConnectionTicketFingerprint != command.ConnectionTicketFingerprint)
+        {
+            return new(StoreResultCode.NotFound);
+        }
+
+        if (!attempt.IntroductionConsumed)
+        {
+            return new(StoreResultCode.Conflict);
+        }
+
+        if (!attempt.TicketDeadline.HasValue || attempt.TicketDeadline.Value <= now)
+        {
+            return new(StoreResultCode.Expired);
+        }
+
+        if (attempt.ConnectionTicketConsumed)
+        {
+            return new(StoreResultCode.ReplayRejected);
+        }
+
+        attempt.ConnectionTicketConsumed = true;
+        return new(StoreResultCode.Success, true);
+    }, cancellationToken);
+
     public StoreResult<bool> ConsumeReplay(
         ReplayConsumption consumption,
         CancellationToken cancellationToken = default) => Atomic<bool>(now =>
@@ -714,10 +819,18 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
         ListingId = entry.Command.ListingId,
         ClientSubject = entry.Command.ClientSubject,
         ProtocolVersion = entry.Command.ProtocolVersion,
+        IdempotencyKey = entry.Command.IdempotencyKey,
+        RequestFingerprint = entry.Command.RequestFingerprint,
+        CapabilityDerivationSalt = entry.Command.CapabilityDerivationSalt,
+        HostCapabilityFingerprint = entry.Command.HostCapabilityFingerprint,
+        ClientCapabilityFingerprint = entry.Command.ClientCapabilityFingerprint,
+        ConnectionTicketFingerprint = entry.Command.ConnectionTicketFingerprint,
         ExpiresAt = entry.WallExpiresAt,
+        ConnectionTicketExpiresAt = entry.TicketWallExpiresAt ?? default,
         HostEndpoint = entry.HostEndpoint,
         ClientEndpoint = entry.ClientEndpoint,
         IntroductionConsumed = entry.IntroductionConsumed,
+        ConnectionTicketConsumed = entry.ConnectionTicketConsumed,
     };
 
     private static void RemoveExpired(Dictionary<string, TimeSpan> entries, TimeSpan now)
@@ -789,6 +902,8 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
             || command.ProtocolVersion == 0
             || !command.HostCapabilityFingerprint.IsValid
             || !command.ClientCapabilityFingerprint.IsValid
+            || !command.ConnectionTicketFingerprint.IsValid
+            || !IsDerivationSaltValid(command.CapabilityDerivationSalt)
             || command.ScopeAttemptLimit <= 0)
         {
             throw new ArgumentException("Join attempt invariants are invalid.", nameof(command));
@@ -853,11 +968,15 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
         public CreateJoinAttemptCommand Command { get; } = command;
         public SecretFingerprint HostCapabilityFingerprint { get; } = command.HostCapabilityFingerprint;
         public SecretFingerprint ClientCapabilityFingerprint { get; } = command.ClientCapabilityFingerprint;
+        public SecretFingerprint ConnectionTicketFingerprint { get; } = command.ConnectionTicketFingerprint;
         public TimeSpan Deadline { get; } = deadline;
         public DateTimeOffset WallExpiresAt { get; } = wallExpiresAt;
+        public TimeSpan? TicketDeadline { get; set; }
+        public DateTimeOffset? TicketWallExpiresAt { get; set; }
         public AttemptEndpointBinding? HostEndpoint { get; set; }
         public AttemptEndpointBinding? ClientEndpoint { get; set; }
         public bool IntroductionConsumed { get; set; }
+        public bool ConnectionTicketConsumed { get; set; }
     }
 
     private sealed record IdempotencyEntry(

src/FinalFactory.Rendezvous.Server/State/StoreResultMapping.cs

@@ -0,0 +1,20 @@
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Server.State;
+
+internal static class StoreResultMapping
+{
+    public static RendezvousErrorCode ToContractError(this StoreResultCode code) => code switch
+    {
+        StoreResultCode.Success => RendezvousErrorCode.None,
+        StoreResultCode.NotFound => RendezvousErrorCode.NotFound,
+        StoreResultCode.Expired => RendezvousErrorCode.Expired,
+        StoreResultCode.Revoked => RendezvousErrorCode.Forbidden,
+        StoreResultCode.Conflict => RendezvousErrorCode.Conflict,
+        StoreResultCode.CapacityExceeded => RendezvousErrorCode.CapacityExceeded,
+        StoreResultCode.ReplayRejected => RendezvousErrorCode.ReplayRejected,
+        StoreResultCode.Draining or StoreResultCode.ServiceUnavailable =>
+            RendezvousErrorCode.ServiceUnavailable,
+        _ => RendezvousErrorCode.InternalError,
+    };
+}

tests/FinalFactory.Rendezvous.Tests/Client/ConnectionTicketValidatorTests.cs

@@ -0,0 +1,102 @@
+using FinalFactory.Rendezvous.Client;
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Tests.Client;
+
+public sealed class ConnectionTicketValidatorTests
+{
+    private static readonly DateTimeOffset Now = new(2026, 7, 16, 12, 0, 0, TimeSpan.Zero);
+
+    [Fact]
+    public void AuthorizedTicketIsAcceptedExactlyOnce()
+    {
+        ManualConnectionTicketClock clock = new();
+        using ConnectionTicketValidator validator = new(1_024, clock);
+        JoinAttemptId attempt = NewAttempt();
+        string ticket = Ticket('A');
+        Assert.True(validator.TryAuthorize(attempt, ticket, Now.AddSeconds(20)));
+        Assert.True(validator.TryAuthorize(attempt, ticket, Now.AddSeconds(20)));
+
+        Assert.Equal(
+            ConnectionTicketConsumptionResult.Accepted,
+            validator.Consume(attempt, ticket));
+        Assert.Equal(
+            ConnectionTicketConsumptionResult.AlreadyConsumed,
+            validator.Consume(attempt, ticket));
+    }
+
+    [Fact]
+    public void AlteredCrossAttemptExpiredAndRevokedTicketsAreRejected()
+    {
+        ManualConnectionTicketClock clock = new();
+        using ConnectionTicketValidator validator = new(1_024, clock);
+        JoinAttemptId first = NewAttempt();
+        JoinAttemptId second = NewAttempt();
+        Assert.True(validator.TryAuthorize(first, Ticket('A'), Now.AddSeconds(20)));
+        Assert.True(validator.TryAuthorize(second, Ticket('B'), Now.AddSeconds(40)));
+
+        Assert.Equal(
+            ConnectionTicketConsumptionResult.Rejected,
+            validator.Consume(first, Ticket('B')));
+        clock.Advance(TimeSpan.FromSeconds(20));
+        Assert.Equal(
+            ConnectionTicketConsumptionResult.Expired,
+            validator.Consume(first, Ticket('A')));
+        Assert.True(validator.Revoke(second));
+        Assert.Equal(
+            ConnectionTicketConsumptionResult.Revoked,
+            validator.Consume(second, Ticket('B')));
+    }
+
+    [Fact]
+    public async Task ConcurrentConsumptionHasOneWinner()
+    {
+        ManualConnectionTicketClock clock = new();
+        using ConnectionTicketValidator validator = new(1_024, clock);
+        JoinAttemptId attempt = NewAttempt();
+        string ticket = Ticket('C');
+        Assert.True(validator.TryAuthorize(attempt, ticket, Now.AddSeconds(20)));
+        using ManualResetEventSlim start = new(false);
+        Task<ConnectionTicketConsumptionResult> left = Task.Run(() =>
+        {
+            start.Wait();
+            return validator.Consume(attempt, ticket);
+        });
+        Task<ConnectionTicketConsumptionResult> right = Task.Run(() =>
+        {
+            start.Wait();
+            return validator.Consume(attempt, ticket);
+        });
+
+        start.Set();
+        ConnectionTicketConsumptionResult[] results = await Task.WhenAll(left, right);
+
+        Assert.Single(results, static result => result == ConnectionTicketConsumptionResult.Accepted);
+        Assert.Single(results, static result => result == ConnectionTicketConsumptionResult.AlreadyConsumed);
+    }
+
+    [Fact]
+    public void ValidatorIsBoundedDisposableAndRedacted()
+    {
+        ManualConnectionTicketClock clock = new();
+        ConnectionTicketValidator validator = new(1, clock);
+        Assert.True(validator.TryAuthorize(NewAttempt(), Ticket('A'), Now.AddSeconds(20)));
+        Assert.False(validator.TryAuthorize(NewAttempt(), Ticket('B'), Now.AddSeconds(20)));
+        Assert.DoesNotContain(Ticket('A'), validator.ToString(), StringComparison.Ordinal);
+
+        validator.Dispose();
+
+        Assert.Throws<ObjectDisposedException>(() => validator.Revoke(NewAttempt()));
+        Assert.Throws<ObjectDisposedException>(() => validator.Consume(default, string.Empty));
+    }
+
+    private static JoinAttemptId NewAttempt() => new(Guid.NewGuid());
+    private static string Ticket(char value) => new(value, 43);
+
+    private sealed class ManualConnectionTicketClock : IConnectionTicketClock
+    {
+        public DateTimeOffset UtcNow { get; set; } = Now;
+
+        public void Advance(TimeSpan duration) => UtcNow += duration;
+    }
+}

tests/FinalFactory.Rendezvous.Tests/Contracts/OpenApiCompatibilityTests.cs

@@ -9,6 +9,7 @@ public sealed class OpenApiCompatibilityTests
         "/health/live",
         "/health/ready",
         "/v1/join-attempts",
+        "/v1/join-attempts/{attemptId}",
         "/v1/join-attempts/{attemptId}/outcome",
         "/v1/sessions",
         "/v1/sessions/{listingId}",
@@ -85,5 +86,23 @@ public sealed class OpenApiCompatibilityTests
                 .GetProperty("security");
             Assert.True(security[0].TryGetProperty("PublisherBearer", out _));
         }
+
+        JsonElement cancelParameters = root.GetProperty("paths")
+            .GetProperty("/v1/join-attempts/{attemptId}")
+            .GetProperty("delete")
+            .GetProperty("parameters");
+        JsonElement cancelCapability = Assert.Single(cancelParameters.EnumerateArray(), static parameter =>
+            parameter.GetProperty("in").GetString() == "header"
+            && parameter.GetProperty("name").GetString()
+                == "X-Rendezvous-Client-Punch-Capability");
+        Assert.True(cancelCapability.GetProperty("required").GetBoolean());
+        JsonElement hostPollParameters = root.GetProperty("paths")
+            .GetProperty("/v1/sessions/{listingId}/join-attempts")
+            .GetProperty("get")
+            .GetProperty("parameters");
+        JsonElement leaseToken = Assert.Single(hostPollParameters.EnumerateArray(), static parameter =>
+            parameter.GetProperty("in").GetString() == "header"
+            && parameter.GetProperty("name").GetString() == "X-Rendezvous-Lease-Token");
+        Assert.True(leaseToken.GetProperty("required").GetBoolean());
     }
 }

tests/FinalFactory.Rendezvous.Tests/JoinAttempts/JoinAttemptHttpEndpointTests.cs

@@ -0,0 +1,204 @@
+using System.Net;
+using System.Net.Http.Json;
+using FinalFactory.Rendezvous.Client;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Browser;
+using FinalFactory.Rendezvous.Server.Http;
+using FinalFactory.Rendezvous.Server.JoinAttempts;
+using FinalFactory.Rendezvous.Server.Provisioning;
+using FinalFactory.Rendezvous.Server.Sessions;
+using FinalFactory.Rendezvous.Server.State;
+using FinalFactory.Rendezvous.Tests.Provisioning;
+using FinalFactory.Rendezvous.Tests.State;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Hosting.Server;
+using Microsoft.AspNetCore.Hosting.Server.Features;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace FinalFactory.Rendezvous.Tests.JoinAttempts;
+
+public sealed class JoinAttemptHttpEndpointTests
+{
+    [Fact]
+    public async Task ClientCreatesHostPollsAndCapabilityCancelsAnAttemptOverHttp()
+    {
+        await using JoinHttpTestHost host = await JoinHttpTestHost.StartAsync();
+        RendezvousPublisherClient publisher = new(host.HttpClient);
+        PublishedSession session = AssertSuccess(await publisher.RegisterAsync(
+            CreateRegistration(),
+            host.PublisherCredential));
+        Assert.True(host.Capabilities.TryFingerprint(
+            session.HostPresenceCapability,
+            out SecretFingerprint presenceFingerprint));
+        Assert.True(host.Store.BindHostPresence(new(
+            session.HostPresenceHandle,
+            presenceFingerprint,
+            new(AddressFamilyKind.Ipv4, "203.0.113.80", 41_000),
+            null)).Succeeded);
+        CreateJoinAttemptRequest request = new()
+        {
+            IdempotencyKey = "http-join-1",
+            GameId = new("space-game"),
+            EnvironmentId = new("production"),
+            ListingId = session.ListingId,
+            ProtocolVersion = 7,
+        };
+
+        using HttpResponseMessage createdResponse = await host.HttpClient.PostAsJsonAsync(
+            "v1/join-attempts",
+            request,
+            ContractJson.Options);
+        Assert.Equal(HttpStatusCode.Created, createdResponse.StatusCode);
+        CreateJoinAttemptResponse created = Assert.IsType<CreateJoinAttemptResponse>(
+            await createdResponse.Content.ReadFromJsonAsync<CreateJoinAttemptResponse>(ContractJson.Options));
+
+        using HttpRequestMessage pollRequest = new(
+            HttpMethod.Get,
+            $"v1/sessions/{session.ListingId}/join-attempts?contractVersion=1&pageSize=10");
+        pollRequest.Headers.Add("X-Rendezvous-Lease-Token", session.LeaseToken);
+        using HttpResponseMessage pollResponse = await host.HttpClient.SendAsync(pollRequest);
+        Assert.Equal(HttpStatusCode.OK, pollResponse.StatusCode);
+        BrowseHostJoinAttemptsResponse polled = Assert.IsType<BrowseHostJoinAttemptsResponse>(
+            await pollResponse.Content.ReadFromJsonAsync<BrowseHostJoinAttemptsResponse>(ContractJson.Options));
+        HostJoinAttempt hostAttempt = Assert.Single(polled.Items);
+        Assert.Equal(created.AttemptId, hostAttempt.AttemptId);
+        Assert.NotEqual(created.ClientPunchCapability, hostAttempt.HostPunchCapability);
+
+        using HttpResponseMessage missingCapability = await host.HttpClient.DeleteAsync(
+            $"v1/join-attempts/{created.AttemptId}");
+        Assert.Equal(HttpStatusCode.BadRequest, missingCapability.StatusCode);
+        ApiError missingCapabilityError = Assert.IsType<ApiError>(
+            await missingCapability.Content.ReadFromJsonAsync<ApiError>(ContractJson.Options));
+        Assert.Equal(RendezvousErrorCode.InvalidRequest, missingCapabilityError.Code);
+
+        using HttpRequestMessage unauthorizedCancel = new(
+            HttpMethod.Delete,
+            $"v1/join-attempts/{created.AttemptId}");
+        unauthorizedCancel.Headers.Add(
+            "X-Rendezvous-Client-Punch-Capability",
+            "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA");
+        using HttpResponseMessage unauthorized = await host.HttpClient.SendAsync(unauthorizedCancel);
+        Assert.Equal(HttpStatusCode.NotFound, unauthorized.StatusCode);
+
+        using HttpRequestMessage cancelRequest = new(
+            HttpMethod.Delete,
+            $"v1/join-attempts/{created.AttemptId}");
+        cancelRequest.Headers.Add(
+            "X-Rendezvous-Client-Punch-Capability",
+            created.ClientPunchCapability);
+        using HttpResponseMessage cancelled = await host.HttpClient.SendAsync(cancelRequest);
+        Assert.Equal(HttpStatusCode.NoContent, cancelled.StatusCode);
+
+        using HttpRequestMessage emptyPollRequest = new(
+            HttpMethod.Get,
+            $"v1/sessions/{session.ListingId}/join-attempts?contractVersion=1&pageSize=10");
+        emptyPollRequest.Headers.Add("X-Rendezvous-Lease-Token", session.LeaseToken);
+        using HttpResponseMessage emptyPollResponse = await host.HttpClient.SendAsync(emptyPollRequest);
+        BrowseHostJoinAttemptsResponse empty = Assert.IsType<BrowseHostJoinAttemptsResponse>(
+            await emptyPollResponse.Content.ReadFromJsonAsync<BrowseHostJoinAttemptsResponse>(ContractJson.Options));
+        Assert.Empty(empty.Items);
+    }
+
+    private static T AssertSuccess<T>(RendezvousClientResult<T> result)
+    {
+        Assert.True(result.IsSuccess, result.Message);
+        return Assert.IsAssignableFrom<T>(result.Value);
+    }
+
+    private static RegisterSessionRequest CreateRegistration() => new()
+    {
+        IdempotencyKey = "join-http-host",
+        GameId = new("space-game"),
+        EnvironmentId = new("production"),
+        RegionId = new("eu-central"),
+        ProtocolVersion = 7,
+        BuildVersion = "1.0.0",
+        DisplayName = "Join HTTP host",
+        Visibility = ListingVisibility.Public,
+        Capacity = new() { CurrentPlayers = 8, MaximumPlayers = 8 },
+        Metadata = new() { ["mode"] = "online-coop" },
+    };
+
+    private sealed class JoinHttpTestHost : IAsyncDisposable
+    {
+        private readonly WebApplication _application;
+
+        private JoinHttpTestHost(
+            WebApplication application,
+            HttpClient httpClient,
+            InMemoryEphemeralRendezvousStore store,
+            EphemeralCapabilityIssuer capabilities,
+            string publisherCredential)
+        {
+            _application = application;
+            HttpClient = httpClient;
+            Store = store;
+            Capabilities = capabilities;
+            PublisherCredential = publisherCredential;
+        }
+
+        internal HttpClient HttpClient { get; }
+        internal InMemoryEphemeralRendezvousStore Store { get; }
+        internal EphemeralCapabilityIssuer Capabilities { get; }
+        internal string PublisherCredential { get; }
+
+        internal static async Task<JoinHttpTestHost> StartAsync()
+        {
+            ManualRendezvousClock clock = new(ProvisioningTestData.Now);
+            EphemeralStoreOptions stateOptions = new();
+            InMemoryEphemeralRendezvousStore store = new(stateOptions, clock, clock);
+            EphemeralCapabilityIssuer capabilities = new();
+            ProvisioningRuntime provisioning = ProvisioningRuntime.Create(
+                ProvisioningTestData.CreateOptions(),
+                ProvisioningTestData.CreateSecrets("secret-1"),
+                clock.UtcNow);
+            DedicatedPublisherPrincipal principal = ProvisioningTestData.CreateDedicatedPublisher();
+            string credential = provisioning.Credentials.Issue(principal, clock.UtcNow);
+
+            WebApplicationBuilder builder = WebApplication.CreateBuilder();
+            builder.WebHost.UseUrls("http://127.0.0.1:0");
+            builder.Services.ConfigureHttpJsonOptions(static options =>
+                ContractJson.Configure(options.SerializerOptions));
+            builder.Services.Configure<RouteHandlerOptions>(static options =>
+                options.ThrowOnBadRequest = true);
+            builder.Services.AddProblemDetails();
+            builder.Services.AddExceptionHandler<RendezvousExceptionHandler>();
+            builder.Services.AddSingleton(provisioning);
+            builder.Services.AddSingleton(provisioning.Policies);
+            builder.Services.AddSingleton(provisioning.Credentials);
+            builder.Services.AddSingleton(provisioning.PublisherAuthorization);
+            builder.Services.AddSingleton<IEphemeralRendezvousStore>(store);
+            builder.Services.AddSingleton<IWallClock>(clock);
+            builder.Services.AddSingleton(capabilities);
+            builder.Services.AddSingleton<ISessionCapabilityService>(capabilities);
+            builder.Services.AddSingleton(SessionLeaseTiming.From(stateOptions));
+            builder.Services.AddSingleton<SessionLeaseService>();
+            builder.Services.AddSingleton<SessionBrowserCursorCodec>();
+            builder.Services.AddSingleton<SessionBrowserService>();
+            builder.Services.AddSingleton<JoinAttemptCursorCodec>();
+            builder.Services.AddSingleton<JoinAttemptService>();
+
+            WebApplication app = builder.Build();
+            app.UseExceptionHandler();
+            app.MapRendezvousContractEndpoints();
+            await app.StartAsync();
+            IServer server = app.Services.GetRequiredService<IServer>();
+            string address = Assert.Single(server.Features.Get<IServerAddressesFeature>()!.Addresses);
+            return new(
+                app,
+                new HttpClient { BaseAddress = new Uri(address) },
+                store,
+                capabilities,
+                credential);
+        }
+
+        public async ValueTask DisposeAsync()
+        {
+            HttpClient.Dispose();
+            await _application.StopAsync();
+            await _application.DisposeAsync();
+        }
+    }
+}

tests/FinalFactory.Rendezvous.Tests/JoinAttempts/JoinAttemptServiceTests.cs

@@ -0,0 +1,286 @@
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.JoinAttempts;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Tests.JoinAttempts;
+
+public sealed class JoinAttemptServiceTests
+{
+    [Fact]
+    public void CreateIsIdempotentAndScopesDistinctRoleCredentials()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        CreateJoinAttemptRequest request = fixture.Request(registration.ListingId, "stable-join-key");
+
+        JoinAttemptServiceResult<CreateJoinAttemptResponse> first = fixture.Service.Create(
+            fixture.ClientSubject,
+            request);
+        JoinAttemptServiceResult<CreateJoinAttemptResponse> replay = fixture.Service.Create(
+            fixture.ClientSubject,
+            request);
+
+        Assert.True(first.Succeeded);
+        Assert.True(replay.Succeeded);
+        Assert.Equal(first.Value!.AttemptId, replay.Value!.AttemptId);
+        Assert.Equal(first.Value.MediationHandle, replay.Value.MediationHandle);
+        Assert.Equal(first.Value.ClientPunchCapability, replay.Value.ClientPunchCapability);
+        Assert.True(ContractValidation.IsCapabilityValid(first.Value.ClientPunchCapability));
+        Assert.InRange(
+            first.Value.ClientPunchCapability.Length,
+            1,
+            ContractLimits.LiteNetLibNatTokenMaxCharacters);
+
+        HostJoinAttempt host = Assert.Single(fixture.Service.BrowseForHost(
+            registration.ListingId,
+            ContractLimits.ContractVersion,
+            registration.LeaseToken,
+            10,
+            null).Value!.Items);
+        Assert.NotEqual(host.HostPunchCapability, first.Value.ClientPunchCapability);
+        Assert.DoesNotContain(first.Value.ClientPunchCapability, fixture.Sessions.Store.ToString(), StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void SameIdempotencyKeyWithDifferentRequestConflicts()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        (RegisterSessionResponse other, _) = fixture.CreateHost();
+        CreateJoinAttemptRequest request = fixture.Request(registration.ListingId, "reused-key");
+        Assert.True(fixture.Service.Create(fixture.ClientSubject, request).Succeeded);
+
+        request.ListingId = other.ListingId;
+        JoinAttemptServiceResult<CreateJoinAttemptResponse> conflict = fixture.Service.Create(
+            fixture.ClientSubject,
+            request);
+
+        Assert.Equal(RendezvousErrorCode.Conflict, conflict.Error);
+    }
+
+    [Fact]
+    public void CreationRejectsStaleIncompatibleAndCrossTenantListings()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse stale, _) = fixture.CreateHost(bindPresence: false);
+        Assert.Equal(
+            RendezvousErrorCode.NotFound,
+            fixture.Service.Create(fixture.ClientSubject, fixture.Request(stale.ListingId)).Error);
+
+        (RegisterSessionResponse active, _) = fixture.CreateHost();
+        CreateJoinAttemptRequest incompatible = fixture.Request(active.ListingId);
+        incompatible.ProtocolVersion = 8;
+        Assert.Equal(
+            RendezvousErrorCode.IncompatibleProtocol,
+            fixture.Service.Create(fixture.ClientSubject, incompatible).Error);
+
+        CreateJoinAttemptRequest otherTenant = fixture.Request(active.ListingId);
+        otherTenant.GameId = new("other-game");
+        Assert.Equal(
+            RendezvousErrorCode.NotFound,
+            fixture.Service.Create(fixture.ClientSubject, otherTenant).Error);
+    }
+
+    [Fact]
+    public void HostPollingAuthenticatesLeaseAndUsesScopeBoundCursorPaging()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        fixture.Create(registration.ListingId);
+        fixture.Create(registration.ListingId);
+        fixture.Create(registration.ListingId);
+
+        JoinAttemptServiceResult<BrowseHostJoinAttemptsResponse> first = fixture.Service.BrowseForHost(
+            registration.ListingId,
+            ContractLimits.ContractVersion,
+            registration.LeaseToken,
+            1,
+            null);
+        Assert.True(first.Succeeded);
+        Assert.Single(first.Value!.Items);
+        Assert.NotNull(first.Value.NextCursor);
+
+        JoinAttemptServiceResult<BrowseHostJoinAttemptsResponse> second = fixture.Service.BrowseForHost(
+            registration.ListingId,
+            ContractLimits.ContractVersion,
+            registration.LeaseToken,
+            1,
+            first.Value.NextCursor);
+        Assert.True(second.Succeeded);
+        Assert.NotEqual(first.Value.Items[0].AttemptId, second.Value!.Items[0].AttemptId);
+
+        Assert.Equal(
+            RendezvousErrorCode.NotFound,
+            fixture.Service.BrowseForHost(
+                registration.ListingId,
+                ContractLimits.ContractVersion,
+                "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
+                1,
+                null).Error);
+        Assert.Equal(
+            RendezvousErrorCode.InvalidRequest,
+            fixture.Service.BrowseForHost(
+                registration.ListingId,
+                ContractLimits.ContractVersion,
+                registration.LeaseToken,
+                1,
+                first.Value.NextCursor + "x").Error);
+
+        (RegisterSessionResponse other, _) = fixture.CreateHost();
+        Assert.Equal(
+            RendezvousErrorCode.InvalidRequest,
+            fixture.Service.BrowseForHost(
+                other.ListingId,
+                ContractLimits.ContractVersion,
+                other.LeaseToken,
+                1,
+                first.Value.NextCursor).Error);
+    }
+
+    [Fact]
+    public void CancellationRequiresTheAttemptsClientCapabilityAndRevokesState()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        CreateJoinAttemptResponse created = fixture.Create(registration.ListingId);
+
+        Assert.Equal(
+            RendezvousErrorCode.NotFound,
+            fixture.Service.Cancel(
+                created.AttemptId,
+                "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA").Error);
+        Assert.True(fixture.Service.Cancel(
+            created.AttemptId,
+            created.ClientPunchCapability).Succeeded);
+        Assert.Empty(fixture.Service.BrowseForHost(
+            registration.ListingId,
+            ContractLimits.ContractVersion,
+            registration.LeaseToken,
+            10,
+            null).Value!.Items);
+    }
+
+    [Fact]
+    public void RoleAndAttemptCapabilitiesCannotCrossWireConcurrentAttempts()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        CreateJoinAttemptResponse first = fixture.Create(registration.ListingId);
+        CreateJoinAttemptResponse second = fixture.Create(registration.ListingId);
+        StoredJoinAttempt firstStored = fixture.GetAttempt(registration, first.AttemptId);
+        Assert.True(fixture.Sessions.Capabilities.TryFingerprint(
+            second.ClientPunchCapability,
+            out SecretFingerprint secondClientFingerprint));
+        Assert.True(fixture.Sessions.Capabilities.TryFingerprint(
+            first.ClientPunchCapability,
+            out SecretFingerprint firstClientFingerprint));
+
+        Assert.Equal(
+            StoreResultCode.NotFound,
+            fixture.Sessions.Store.BindAttemptEndpoint(new(
+                firstStored.MediationHandle,
+                AttemptPeerRole.Client,
+                secondClientFingerprint,
+                new(AddressFamilyKind.Ipv4, "198.51.100.20", 42_000),
+                null)).Code);
+        Assert.Equal(
+            StoreResultCode.NotFound,
+            fixture.Sessions.Store.BindAttemptEndpoint(new(
+                firstStored.MediationHandle,
+                AttemptPeerRole.Host,
+                firstClientFingerprint,
+                new(AddressFamilyKind.Ipv4, "203.0.113.20", 41_000),
+                null)).Code);
+    }
+
+    [Fact]
+    public async Task ConnectionTicketIsDistinctExpiringAndAtomicallySingleUse()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        CreateJoinAttemptResponse created = fixture.Create(registration.ListingId);
+        IntroductionEndpoints introduction = fixture.Introduce(registration, created);
+        JoinAttemptServiceResult<ConnectionTicketGrant> issued = fixture.Service.IssueConnectionTicket(
+            introduction.Attempt);
+        Assert.True(issued.Succeeded);
+        Assert.True(ContractValidation.IsConnectionTicketValid(issued.Value!.Ticket));
+        Assert.NotEqual(created.ClientPunchCapability, issued.Value.Ticket);
+        Assert.DoesNotContain(issued.Value.Ticket, issued.Value.ToString(), StringComparison.Ordinal);
+        Assert.True(fixture.Sessions.Capabilities.TryFingerprint(
+            issued.Value.Ticket,
+            out SecretFingerprint ticketFingerprint));
+        ConsumeConnectionTicketCommand command = new(created.AttemptId, ticketFingerprint);
+        using ManualResetEventSlim start = new(false);
+
+        Task<StoreResult<bool>> left = Task.Run(() =>
+        {
+            start.Wait();
+            return fixture.Sessions.Store.ConsumeConnectionTicket(command);
+        });
+        Task<StoreResult<bool>> right = Task.Run(() =>
+        {
+            start.Wait();
+            return fixture.Sessions.Store.ConsumeConnectionTicket(command);
+        });
+        start.Set();
+        StoreResult<bool>[] results = await Task.WhenAll(left, right);
+
+        Assert.Single(results, static result => result.Succeeded);
+        Assert.Single(results, static result => result.Code == StoreResultCode.ReplayRejected);
+    }
+
+    [Fact]
+    public void TicketRejectsAlteredCrossAttemptPreIntroductionAndExpiry()
+    {
+        EphemeralStoreOptions options = new()
+        {
+            ConnectionTicketLifetime = TimeSpan.FromSeconds(5),
+        };
+        using JoinAttemptFixture fixture = new(options);
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        CreateJoinAttemptResponse first = fixture.Create(registration.ListingId);
+        CreateJoinAttemptResponse second = fixture.Create(registration.ListingId);
+        StoredJoinAttempt firstStored = fixture.GetAttempt(registration, first.AttemptId);
+        StoredJoinAttempt secondStored = fixture.GetAttempt(registration, second.AttemptId);
+
+        Assert.Equal(
+            StoreResultCode.Conflict,
+            fixture.Sessions.Store.ConsumeConnectionTicket(new(
+                first.AttemptId,
+                firstStored.ConnectionTicketFingerprint)).Code);
+        Assert.Equal(
+            StoreResultCode.NotFound,
+            fixture.Sessions.Store.ConsumeConnectionTicket(new(
+                second.AttemptId,
+                firstStored.ConnectionTicketFingerprint)).Code);
+
+        fixture.Introduce(registration, first);
+        fixture.Sessions.Clock.Advance(options.ConnectionTicketLifetime);
+        Assert.Equal(
+            StoreResultCode.Expired,
+            fixture.Sessions.Store.ConsumeConnectionTicket(new(
+                first.AttemptId,
+                firstStored.ConnectionTicketFingerprint)).Code);
+        Assert.False(secondStored.ConnectionTicketConsumed);
+    }
+
+    [Fact]
+    public void TicketWindowBeginsAtIntroductionAndNeverOutlivesTheAttempt()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        CreateJoinAttemptResponse created = fixture.Create(registration.ListingId);
+        fixture.Sessions.Clock.Advance(TimeSpan.FromSeconds(15));
+
+        IntroductionEndpoints introduction = fixture.Introduce(registration, created);
+        ConnectionTicketGrant ticket = Assert.IsType<ConnectionTicketGrant>(
+            fixture.Service.IssueConnectionTicket(introduction.Attempt).Value);
+
+        Assert.Equal(created.ExpiresAt, ticket.ExpiresAt);
+        Assert.Equal(TimeSpan.FromSeconds(15), ticket.ExpiresAt - fixture.Sessions.Clock.UtcNow);
+        Assert.DoesNotContain(
+            introduction.Attempt.CapabilityDerivationSalt,
+            introduction.Attempt.ToString(),
+            StringComparison.Ordinal);
+    }
+}

tests/FinalFactory.Rendezvous.Tests/JoinAttempts/JoinAttemptTestData.cs

@@ -0,0 +1,117 @@
+using System.Net;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.JoinAttempts;
+using FinalFactory.Rendezvous.Server.Provisioning;
+using FinalFactory.Rendezvous.Server.State;
+using FinalFactory.Rendezvous.Tests.Provisioning;
+using FinalFactory.Rendezvous.Tests.Sessions;
+
+namespace FinalFactory.Rendezvous.Tests.JoinAttempts;
+
+internal sealed class JoinAttemptFixture : IDisposable
+{
+    private int _sequence;
+
+    public JoinAttemptFixture(EphemeralStoreOptions? options = null)
+    {
+        Sessions = new(options);
+        Cursors = new();
+        GamePolicyRegistry policies = GamePolicyRegistry.Create([ProvisioningTestData.CreatePolicy()]);
+        Service = new(policies, Sessions.Store, Sessions.Capabilities, Cursors, Sessions.Clock);
+        ClientSubject = Service.CreateAnonymousClientSubject(IPAddress.Parse("198.51.100.40"));
+    }
+
+    public SessionLeaseFixture Sessions { get; }
+    public JoinAttemptCursorCodec Cursors { get; }
+    public JoinAttemptService Service { get; }
+    public string ClientSubject { get; }
+
+    public (RegisterSessionResponse Registration, StoredListing Listing) CreateHost(bool bindPresence = true)
+    {
+        RegisterSessionResponse registration = Sessions.Register();
+        if (bindPresence)
+        {
+            Assert.True(Sessions.BindPresence(registration).Succeeded);
+        }
+
+        StoredListing listing = Sessions.Store.GetListing(registration.ListingId, false).Value!;
+        return (registration, listing);
+    }
+
+    public CreateJoinAttemptRequest Request(
+        SessionListingId listingId,
+        string? idempotencyKey = null) => new()
+        {
+            IdempotencyKey = idempotencyKey ?? $"join-{Interlocked.Increment(ref _sequence)}",
+            GameId = Sessions.Scope.GameId,
+            EnvironmentId = Sessions.Scope.EnvironmentId,
+            ListingId = listingId,
+            ProtocolVersion = 7,
+        };
+
+    public CreateJoinAttemptResponse Create(
+        SessionListingId listingId,
+        string? idempotencyKey = null)
+    {
+        JoinAttemptServiceResult<CreateJoinAttemptResponse> result = Service.Create(
+            ClientSubject,
+            Request(listingId, idempotencyKey));
+        Assert.True(result.Succeeded);
+        return Assert.IsType<CreateJoinAttemptResponse>(result.Value);
+    }
+
+    public StoredJoinAttempt GetAttempt(
+        RegisterSessionResponse registration,
+        JoinAttemptId attemptId)
+    {
+        Assert.True(Sessions.Capabilities.TryFingerprint(
+            registration.LeaseToken,
+            out SecretFingerprint leaseFingerprint));
+        IReadOnlyList<StoredJoinAttempt> attempts = Sessions.Store.BrowseHostJoinAttempts(new(
+            registration.ListingId,
+            leaseFingerprint,
+            ContractLimits.BrowserPageMaxItems)).Value!;
+        return attempts.Single(attempt => attempt.AttemptId == attemptId);
+    }
+
+    public IntroductionEndpoints Introduce(
+        RegisterSessionResponse registration,
+        CreateJoinAttemptResponse created)
+    {
+        StoredJoinAttempt attempt = GetAttempt(registration, created.AttemptId);
+        HostJoinAttempt host = Service.BrowseForHost(
+            registration.ListingId,
+            ContractLimits.ContractVersion,
+            registration.LeaseToken,
+            ContractLimits.BrowserPageMaxItems,
+            null).Value!.Items.Single(item => item.AttemptId == created.AttemptId);
+        Assert.True(Sessions.Capabilities.TryFingerprint(
+            host.HostPunchCapability,
+            out SecretFingerprint hostFingerprint));
+        Assert.True(Sessions.Capabilities.TryFingerprint(
+            created.ClientPunchCapability,
+            out SecretFingerprint clientFingerprint));
+        Assert.True(Sessions.Store.BindAttemptEndpoint(new(
+            attempt.MediationHandle,
+            AttemptPeerRole.Host,
+            hostFingerprint,
+            new(AddressFamilyKind.Ipv4, "203.0.113.20", 41_000),
+            null)).Succeeded);
+        Assert.True(Sessions.Store.BindAttemptEndpoint(new(
+            attempt.MediationHandle,
+            AttemptPeerRole.Client,
+            clientFingerprint,
+            new(AddressFamilyKind.Ipv4, "198.51.100.40", 42_000),
+            null)).Succeeded);
+        StoreResult<IntroductionEndpoints> introduced = Sessions.Store.ConsumeIntroduction(
+            attempt.MediationHandle);
+        Assert.True(introduced.Succeeded);
+        return introduced.Value!;
+    }
+
+    public void Dispose()
+    {
+        Cursors.Dispose();
+        Sessions.Dispose();
+    }
+}

tests/FinalFactory.Rendezvous.Tests/Provisioning/PrincipalCredentialTests.cs

@@ -5,6 +5,15 @@ namespace FinalFactory.Rendezvous.Tests.Provisioning;
 
 public sealed class PrincipalCredentialTests
 {
+    [Fact]
+    public void Base64UrlDecoderRejectsNonCanonicalTrailingBits()
+    {
+        Assert.True(Base64Url.TryDecode("AA", out byte[] canonical));
+        Assert.Equal(new byte[] { 0 }, canonical);
+        Assert.False(Base64Url.TryDecode("AB", out byte[] nonCanonical));
+        Assert.Empty(nonCanonical);
+    }
+
     [Fact]
     public void DedicatedAndPlayerGrantCredentialsRoundtripToDistinctPrincipals()
     {

tests/FinalFactory.Rendezvous.Tests/Sessions/SessionLeaseServiceTests.cs

@@ -61,6 +61,7 @@ public sealed class SessionLeaseServiceTests
         {
             LeaseLifetime = TimeSpan.FromSeconds(5),
             JoinAttemptLifetime = TimeSpan.FromSeconds(5),
+            ConnectionTicketLifetime = TimeSpan.FromSeconds(5),
             IdempotencyLifetime = TimeSpan.FromSeconds(6),
         };
         using SessionLeaseFixture fixture = new(options);

tests/FinalFactory.Rendezvous.Tests/State/EphemeralStateTestData.cs

@@ -95,6 +95,8 @@ internal sealed class EphemeralStateFixture
             ProtocolVersion = listing.Definition.ProtocolVersion,
             HostCapabilityFingerprint = Fingerprint($"host-{sequence}"),
             ClientCapabilityFingerprint = Fingerprint($"client-{sequence}"),
+            ConnectionTicketFingerprint = Fingerprint($"ticket-{sequence}"),
+            CapabilityDerivationSalt = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
         };
     }
 

tests/FinalFactory.Rendezvous.Tests/State/StoreResultMappingTests.cs

@@ -0,0 +1,30 @@
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Tests.State;
+
+public sealed class StoreResultMappingTests
+{
+    [Fact]
+    public void EveryStoreResultHasOneSharedContractErrorMapping()
+    {
+        Dictionary<StoreResultCode, RendezvousErrorCode> expected = new()
+        {
+            [StoreResultCode.Success] = RendezvousErrorCode.None,
+            [StoreResultCode.NotFound] = RendezvousErrorCode.NotFound,
+            [StoreResultCode.Expired] = RendezvousErrorCode.Expired,
+            [StoreResultCode.Revoked] = RendezvousErrorCode.Forbidden,
+            [StoreResultCode.Conflict] = RendezvousErrorCode.Conflict,
+            [StoreResultCode.CapacityExceeded] = RendezvousErrorCode.CapacityExceeded,
+            [StoreResultCode.Draining] = RendezvousErrorCode.ServiceUnavailable,
+            [StoreResultCode.ReplayRejected] = RendezvousErrorCode.ReplayRejected,
+            [StoreResultCode.ServiceUnavailable] = RendezvousErrorCode.ServiceUnavailable,
+        };
+
+        Assert.Equal(Enum.GetValues<StoreResultCode>().Length, expected.Count);
+        foreach (KeyValuePair<StoreResultCode, RendezvousErrorCode> item in expected)
+        {
+            Assert.Equal(item.Value, item.Key.ToContractError());
+        }
+    }
+}

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/client-public-api.txt

@@ -1,3 +1,17 @@
+TYPE FinalFactory.Rendezvous.Client.ConnectionTicketConsumptionResult
+  ENUM Accepted=1
+  ENUM NotFound=2
+  ENUM Expired=3
+  ENUM Rejected=4
+  ENUM AlreadyConsumed=5
+  ENUM Revoked=6
+TYPE FinalFactory.Rendezvous.Client.ConnectionTicketValidator
+  CTOR (System.Int32 maximumAuthorizedTickets)
+  METHOD FinalFactory.Rendezvous.Client.ConnectionTicketConsumptionResult Consume(FinalFactory.Rendezvous.Contracts.JoinAttemptId attemptId, System.String connectionTicket)
+  METHOD System.Void Dispose()
+  METHOD System.Boolean Revoke(FinalFactory.Rendezvous.Contracts.JoinAttemptId attemptId)
+  METHOD System.String ToString()
+  METHOD System.Boolean TryAuthorize(FinalFactory.Rendezvous.Contracts.JoinAttemptId attemptId, System.String connectionTicket, System.DateTimeOffset expiresAt)
 TYPE FinalFactory.Rendezvous.Client.IRendezvousDelay
   METHOD System.Threading.Tasks.Task DelayAsync(System.TimeSpan delay, System.Threading.CancellationToken cancellationToken)
 TYPE FinalFactory.Rendezvous.Client.IRendezvousPublisherClient