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

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


## Backport

This needs to be back ported to the v1.x branch.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -17,6 +17,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### 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. (#3564)
 - Fixed regression issue in v2.x where `NetworkObject.GetNetworkBehaviourAtOrderIndex` was converted from public to internal. (#3541)
 - Fixed ensuring OnValueChanged callback is still triggered on the authority when a collection changes and then reverts to the previous value in the same frame. (#3539)
 - Fixed synchronizing the destroyGameObject parameter to clients for InScenePlaced network objects. (#3514)

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

@@ -635,7 +635,7 @@ 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

@@ -22,7 +22,7 @@ public enum PlayerCreation
             Prefab,
             PrefabHash,
             NoPlayer,
-            FailValidation
+            FailValidation,
         }
         private PlayerCreation m_PlayerCreation;
         private bool m_ClientDisconnectReasonValidated;
@@ -38,7 +38,7 @@ public ConnectionApprovalTests(PlayerCreation playerCreation)
 
         protected override int NumberOfClients => 1;
 
-        private Guid m_ValidationToken;
+        private string m_ValidationToken;
 
         protected override bool ShouldCheckForSpawnedPlayers()
         {
@@ -56,8 +56,13 @@ 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;
+            // Exceed the expected MTU size
+            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)
@@ -66,7 +71,6 @@ protected override void OnServerAndClientsCreated()
             }
             m_ServerNetworkManager.NetworkConfig.ConnectionApproval = true;
             m_ServerNetworkManager.NetworkConfig.ConnectionData = validationToken;
-
             foreach (var client in m_ClientNetworkManagers)
             {
                 client.NetworkConfig.PlayerPrefab = m_PlayerCreation == PlayerCreation.Prefab ? m_PlayerPrefab : null;