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

Closes #10
2026-07-16 06:56:30 +02:00
parent 06c3973ce7
commit 1baa1055dc
30 changed files with 2057 additions and 113 deletions
@@ -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;
+        }
+    }
+}