Related functions and when they're called:
::onConnectRequest - When the client presses join on the join server screen. It checks to see if the server is full or if they put in the wrong password, or if the user is banned. Cannot be packaged or overwritten.
::onConnected - When the client successfully connects to the server. Cannot be packaged or overwritten. However this instantly calls ::autoAdminCheck which you can package rather than ::onConnected.
::onClientEnterGame - Called once the client finishes loading.
::spawnPlayer - Called when the client spawns or respawns their player.
All of these are GameConnection.