fix: connection approval cannot exceed mtu size - backport (3564) (#3565)

This PR resolves the issue where a NetworkConfig.ConnectionData that
caused the ConnectionRequestMessage to exceed the transport's MTU size
would result in a buffer overflow error by updating
ConnectionRequestMessage to use the ReliableFragmentedSequenced pipeline
as opposed to the ReliableSequenced pipeline.

[MTTB-1467](https://jira.unity3d.com/browse/MTTB-1467)

## Changelog

- Fixed: issue where NetworkConfig.ConnectionData could cause the
ConnectionRequestMessage to exceed the transport's MTU size and would
result in a buffer overflow error.

## Testing and Documentation

- Includes modifications to `ConnectionApproval` integration tests to
use a > MTU size `NetworkConfig.ConnectionData`.
- No documentation changes or additions were necessary.

## Backport

This is a back port of #3564.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -10,6 +10,16 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Added
 
+### Fixed
+
+- Fixed issue where NetworkConfig.ConnectionData could cause the ConnectionRequestMessage to exceed the transport's MTU size and would result in a buffer overflow error. (#3565)
+
+### Changed
+
+## [1.14.0] - 2025-07-21
+
+### Added
+
 - Added serializer for `Pose` (#3540)
 - Added mappings between `ClientId` and `TransportId`. (#3515)
 - Added `SinglePlayerTransport` that provides the ability to start as a host for a single player network session. (#3475)

com.unity.netcode.gameobjects/Runtime/Connection/NetworkConnectionManager.cs

@@ -626,7 +626,7 @@ private void SendConnectionRequest()
                 }
             }
 
-            SendMessage(ref message, NetworkDelivery.ReliableSequenced, NetworkManager.ServerClientId);
+            SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, NetworkManager.ServerClientId);
             message.MessageVersions.Dispose();
         }
 

com.unity.netcode.gameobjects/Tests/Runtime/ConnectionApproval.cs

@@ -34,7 +34,7 @@ public ConnectionApprovalTests(PlayerCreation playerCreation)
 
         protected override int NumberOfClients => 1;
 
-        private Guid m_ValidationToken;
+        private string m_ValidationToken;
 
         protected override bool ShouldCheckForSpawnedPlayers()
         {
@@ -46,8 +46,13 @@ protected override void OnServerAndClientsCreated()
             m_ClientDisconnectReasonValidated = false;
             m_BypassConnectionTimeout = m_PlayerCreation == PlayerCreation.FailValidation;
             m_Validated.Clear();
-            m_ValidationToken = Guid.NewGuid();
-            var validationToken = Encoding.UTF8.GetBytes(m_ValidationToken.ToString());
+            m_ValidationToken = string.Empty;
+
+            while (m_ValidationToken.Length < 2000)
+            {
+                m_ValidationToken += Guid.NewGuid().ToString();
+            }
+            var validationToken = Encoding.UTF8.GetBytes(m_ValidationToken);
             m_ServerNetworkManager.ConnectionApprovalCallback = NetworkManagerObject_ConnectionApprovalCallback;
             m_ServerNetworkManager.NetworkConfig.PlayerPrefab = m_PlayerCreation == PlayerCreation.Prefab ? m_PlayerPrefab : null;
             if (m_PlayerCreation == PlayerCreation.PrefabHash)