What about CGI::Sessions isn't helping? It's not really about authentication. You'd have to think of some way to handle the login. Then you'd store some kind of $is_authenticated token in the session to show they've identified themselves.

If you want to use some relatively dependable authentication mechanisms but you don't want to write something locally, I'd suggest trying Authen::Bitcard. It is the simplest of the single sign on tech that I've tried. All the hard work is done for you. Once they authenticate just store that in the session and you're done.

I am particularly fond of this session setup:
my $ses = new CGI::Session('driver:DB_File;serializer:storable', $cgi);

There may be some security concerns, depending on where you store your flat file, but DB_File (aka Berkely DB) is really nice.