How to determine if a user exists..

I am trying to add another authentication mechanism to PostgreSQL... And,
in doing that, I need to verify the existance of an user within PG. Short
of hacking together code from verify_password(), is there any way to check
if a user exists in postgresql? (The actuall password verification will be
taken care of elsewhere... I just need to check if the user exists.)


thanks,
-- 
Dominic J. Eidson                                       "Baruk Khazad! Khazad ai-menu!" - Gimli
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