From JC2-MP Documentation
|Arguments (in table)||Player player|
Fired when a player becomes fully authenticated by Steam. Until a player is authenticated, it cannot be guaranteed that their identity is genuine.
For example, if you have an admin script that uses Steam ids to give certain players admin access, you should wait until this is fired until they receive access.
function Foo(args) print(args.player:GetName().." has been authenticated by Steam") end Events:Subscribe("PlayerAuthenticate", Foo)