#3731: Update cookie handling with vanilla limits and don't allow unrequested cookies

proxy/src/main/java/net/md_5/bungee/connection/InitialHandler.java

@@ -716,6 +716,10 @@ public class InitialHandler extends PacketHandler implements PendingConnection
 
             throw CancelSendSignal.INSTANCE;
         }
+
+        // if there is no userCon we can't have a connection to a backend server that could have requested this cookie
+        // which means that this cookie is invalid as the proxy also has not requested it
+        Preconditions.checkState( userCon != null, "not requested cookie received" );
     }
 
     @Override