I am by no means an expert in PL/SQL but your function seems ok to me;
your currcal is fine (if you used nextval as someone suggested, you'd get the next value, which is not what you intend, creating user<->groups links.
That said, I ddo not know if doing and insert then asking for curval is atomic or if you could get a wrong value if someone else creates a user at theat moment;
To be on the safe side, I always use insert ... returning syntax this way I know that I am getting the same value as the one inserted.
