I've not looked at your (nor remember looking at MrPresident's) code.
If authed is being called after the password check for the whitelist, you could call ULib.
ucl.addUser if they're not in a group for the whitelist before a kick.
But remember, only use that for "special" server/whitelist guests.
You do NOT want to adduser for a busy server.
Several users of autopromote scripts have ended up in our General Help forum area wondering why the server is unstable, why groups aren't being set correctly.
It's often a few posts into the discussion that we find out they set every user to get promoted to some "regular" group after only a few short hours of playtime, and the users file is hundreds if not thousands of lines long full of "regulars".