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

using System.Collections.Concurrent;
using System.Collections.Frozen;
using System.Security.Cryptography;
using System.Text;
using FinalFactory.Rendezvous.Contracts;

namespace FinalFactory.Rendezvous.Server.Provisioning;

internal sealed class SigningKeyRing : IDisposable
{
    private readonly Dictionary<string, SigningKey> _keys;
    private readonly ConcurrentDictionary<string, byte> _runtimeRevocations =
        new(StringComparer.Ordinal);

    private SigningKeyRing(Dictionary<string, SigningKey> keys) => _keys = keys;

    public bool HasKeys => _keys.Count > 0;

    public static SigningKeyRing Create(
        IEnumerable<SigningKeyOptions> options,
        ISecretProvider secretProvider)
    {
        SigningKeyOptions[] configuredKeys = options.ToArray();
        if (configuredKeys.Length > ProvisioningLimits.MaxSigningKeys)
        {
            throw new ProvisioningConfigurationException(
                $"At most {ProvisioningLimits.MaxSigningKeys} signing keys may be configured.");
        }

        Dictionary<string, SigningKey> keys = new(StringComparer.Ordinal);
        try
        {
            foreach (SigningKeyOptions keyOptions in configuredKeys)
            {
                Validate(keyOptions);
                if (keys.ContainsKey(keyOptions.KeyId))
                {
                    throw new ProvisioningConfigurationException(
                        $"Duplicate signing key ID '{keyOptions.KeyId}'.");
                }

                if (keyOptions.Revoked)
                {
                    keys.Add(keyOptions.KeyId, new SigningKey(keyOptions, null));
                    continue;
                }

                if (!secretProvider.TryGetSecret(
                        keyOptions.SecretReference,
                        out SecretMaterial? material)
                    || material is null)
                {
                    throw new ProvisioningConfigurationException(
                        $"Signing key '{keyOptions.KeyId}' has no available key material.");
                }

                using (material)
                {
                    if (material.Length < 32)
                    {
                        throw new ProvisioningConfigurationException(
                            $"Signing key '{keyOptions.KeyId}' must contain at least 32 bytes.");
                    }

                    keys.Add(keyOptions.KeyId, new SigningKey(keyOptions, material.CopyBytes()));
                }
            }

            return new SigningKeyRing(keys);
        }
        catch
        {
            foreach (SigningKey key in keys.Values)
            {
                key.Dispose();
            }

            throw;
        }
    }

    public bool HasActiveSigningKey(DateTimeOffset now) => _keys.Values.Any(key =>
        !IsRevoked(key)
        && key.NotBefore <= now
        && now < key.SignUntil);

    public bool HasActiveSigningKey(
        DateTimeOffset now,
        PrincipalCredentialKind kind,
        string? gameId,
        string? environmentId) => _keys.Values.Any(key =>
            !IsRevoked(key)
            && key.NotBefore <= now
            && now < key.SignUntil
            && key.Authorizes(kind, gameId, environmentId));

    public bool TryGetSigningKey(
        DateTimeOffset now,
        PrincipalCredentialKind kind,
        string? gameId,
        string? environmentId,
        out SigningKey? signingKey)
    {
        signingKey = _keys.Values
            .Where(key => !IsRevoked(key)
                && key.NotBefore <= now
                && now < key.SignUntil
                && key.Authorizes(kind, gameId, environmentId))
            .OrderByDescending(static key => key.NotBefore)
            .ThenByDescending(static key => key.KeyId, StringComparer.Ordinal)
            .FirstOrDefault();
        return signingKey is not null;
    }

    public VerificationKeyLookup FindVerificationKey(
        string keyId,
        DateTimeOffset now,
        out SigningKey? signingKey)
    {
        signingKey = null;
        if (!_keys.TryGetValue(keyId, out SigningKey? candidate))
        {
            return VerificationKeyLookup.Unknown;
        }

        if (IsRevoked(candidate))
        {
            return VerificationKeyLookup.Revoked;
        }

        if (now < candidate.NotBefore)
        {
            return VerificationKeyLookup.NotYetValid;
        }

        if (now >= candidate.VerifyUntil)
        {
            return VerificationKeyLookup.Retired;
        }

        signingKey = candidate;
        return VerificationKeyLookup.Available;
    }

    public bool Revoke(string keyId) =>
        _keys.ContainsKey(keyId) && _runtimeRevocations.TryAdd(keyId, 0);

    public void Dispose()
    {
        foreach (SigningKey key in _keys.Values)
        {
            key.Dispose();
        }

        _keys.Clear();
        _runtimeRevocations.Clear();
    }

    public override string ToString() => $"[SigningKeyRing: {_keys.Count} keys, material redacted]";

    private bool IsRevoked(SigningKey key) =>
        key.ConfiguredRevoked || _runtimeRevocations.ContainsKey(key.KeyId);

    private static void Validate(SigningKeyOptions options)
    {
        if (string.IsNullOrEmpty(options.KeyId)
            || options.KeyId.Length > 64
            || options.KeyId.Any(static character =>
                character is not (>= 'A' and <= 'Z')
                and not (>= 'a' and <= 'z')
                and not (>= '0' and <= '9')
                and not '-'
                and not '_'))
        {
            throw new ProvisioningConfigurationException(
                "Signing key IDs must be 1–64 base64url characters.");
        }

        if (string.IsNullOrWhiteSpace(options.SecretReference)
            || options.NotBefore >= options.SignUntil
            || options.SignUntil > options.VerifyUntil)
        {
            throw new ProvisioningConfigurationException(
                $"Signing key '{options.KeyId}' has an invalid secret reference or lifetime.");
        }

        if (options.CredentialKinds.Count == 0
            || options.CredentialKinds.Any(static kind => !Enum.IsDefined(kind))
            || options.CredentialKinds.Count != options.CredentialKinds.Distinct().Count())
        {
            throw new ProvisioningConfigurationException(
                $"Signing key '{options.KeyId}' requires unique valid credential kinds.");
        }

        bool operatorKey = options.CredentialKinds.Contains(PrincipalCredentialKind.Operator);
        bool hasPublisherKind = options.CredentialKinds.Any(static kind =>
            kind is PrincipalCredentialKind.DedicatedPublisher
                or PrincipalCredentialKind.PlayerHostGrant);
        if (operatorKey
            ? options.CredentialKinds.Count != 1
                || options.GameId is not null
                || options.EnvironmentId is not null
            : !hasPublisherKind
                || !GameId.TryParse(options.GameId, out _)
                || !EnvironmentId.TryParse(options.EnvironmentId, out _))
        {
            throw new ProvisioningConfigurationException(
                $"Signing key '{options.KeyId}' must be operator-only or bound to one game/environment.");
        }
    }
}

internal sealed class SigningKey : IDisposable
{
    private byte[]? _material;

    public SigningKey(SigningKeyOptions options, byte[]? material)
    {
        KeyId = options.KeyId;
        NotBefore = options.NotBefore;
        SignUntil = options.SignUntil;
        VerifyUntil = options.VerifyUntil;
        ConfiguredRevoked = options.Revoked;
        CredentialKinds = options.CredentialKinds.ToFrozenSet();
        GameId = options.GameId;
        EnvironmentId = options.EnvironmentId;
        _material = material;
    }

    public string KeyId { get; }
    public DateTimeOffset NotBefore { get; }
    public DateTimeOffset SignUntil { get; }
    public DateTimeOffset VerifyUntil { get; }
    public bool ConfiguredRevoked { get; }
    public IReadOnlySet<PrincipalCredentialKind> CredentialKinds { get; }
    public string? GameId { get; }
    public string? EnvironmentId { get; }

    public bool Authorizes(
        PrincipalCredentialKind kind,
        string? gameId,
        string? environmentId) =>
        CredentialKinds.Contains(kind)
        && (kind == PrincipalCredentialKind.Operator
            ? gameId is null && environmentId is null
            : string.Equals(GameId, gameId, StringComparison.Ordinal)
                && string.Equals(EnvironmentId, environmentId, StringComparison.Ordinal));

    public byte[] Sign(string input)
    {
        ObjectDisposedException.ThrowIf(_material is null, this);

        return HMACSHA256.HashData(_material, Encoding.ASCII.GetBytes(input));
    }

    public void Dispose()
    {
        if (_material is not null)
        {
            CryptographicOperations.ZeroMemory(_material);
            _material = null;
        }
    }

    public override string ToString() => $"[SigningKey {KeyId}: material redacted]";
}

internal enum VerificationKeyLookup
{
    Available = 0,
    Unknown = 1,
    Revoked = 2,
    NotYetValid = 3,
    Retired = 4,
}