Added WebRTC stuff - Needs Testing.

RelayServer/Services/ChatTest.cs

@@ -41,6 +41,22 @@ public class ChatTest : WebSocketBehavior
             HandleGetHistory(msg);
             return;
         }
+        
+        SocketRtcSignalMessage? rtcProbe = null;
+        try
+        {
+            rtcProbe = JsonSerializer.Deserialize<SocketRtcSignalMessage>(msg);
+        }
+        catch
+        {
+            // ignored
+        }
+
+        if (rtcProbe?.Type == "encrypted_rtc_signal")
+        {
+            HandleEncryptedRtcSignal(msg);
+            return;
+        }
 
         HandleEncryptedClientMessage(msg);
     }
@@ -323,4 +339,74 @@ public class ChatTest : WebSocketBehavior
 
         return $"{table}:{recordId}";
     }
+    
+    private void HandleEncryptedRtcSignal(string msg)
+    {
+        SocketRtcSignalMessage? clientPayload;
+
+        try
+        {
+            clientPayload = JsonSerializer.Deserialize<SocketRtcSignalMessage>(msg);
+        }
+        catch
+        {
+            Console.WriteLine("Failed to parse encrypted RTC signal payload.");
+            return;
+        }
+
+        if (clientPayload is null || clientPayload.Type != "encrypted_rtc_signal")
+            return;
+
+        if (ClientKeyService is null || string.IsNullOrWhiteSpace(ServerPrivateKey))
+        {
+            Console.WriteLine("Server RTC crypto dependencies are not initialized.");
+            return;
+        }
+
+        string plainJson;
+
+        try
+        {
+            plainJson = E2EeHelper.DecryptForRecipient(
+                new EncryptedPayload
+                {
+                    CipherText = clientPayload.CipherText,
+                    Nonce = clientPayload.Nonce,
+                    Tag = clientPayload.Tag,
+                    EncryptedKey = clientPayload.EncryptedKey
+                },
+                ServerPrivateKey
+            );
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"Failed to decrypt RTC signal payload: {ex.Message}");
+            return;
+        }
+
+        var targetClient = Task.Run(async () => await ClientKeyService.GetByUsernameAsync(clientPayload.RecipientUsername))
+            .GetAwaiter()
+            .GetResult();
+
+        if (targetClient is null)
+        {
+            Console.WriteLine($"No target RTC client key found for {clientPayload.RecipientUsername}");
+            return;
+        }
+
+        var encrypted = E2EeHelper.EncryptForRecipient(plainJson, targetClient.PublicKey);
+
+        var outbound = new SocketRtcSignalMessage
+        {
+            Type = "encrypted_rtc_signal",
+            SenderUsername = clientPayload.SenderUsername,
+            RecipientUsername = clientPayload.RecipientUsername,
+            CipherText = encrypted.CipherText,
+            Nonce = encrypted.Nonce,
+            Tag = encrypted.Tag,
+            EncryptedKey = encrypted.EncryptedKey
+        };
+
+        Sessions.Broadcast(JsonSerializer.Serialize(outbound));
+    }
 }