[Mediawiki-l] external authentication and groups

[GF]

I have written a custom authtentication plugin that works correctly.
Some user in my external user DB are administrators, and i want that also in
mediawiki they should be administrator.
Is there any "clean" way about doing this?

Where can I found the functions to get the groups associated to a user or a
function to add/remove a user to a group?
I think it's not good to directly write into the user_group association
table.

Thank you.