[patrickb]

My solution to the problem is 2-fold.

First, I assume that the authentication is done by your own website.

If the user is authenticated, I do 2 things :

1. Create sessionhash and a userid cookies on the user's client
2. Add the session information to the database

I basically mimic what vBulletin does. You can look into the functions_login.php file and dig through it to see what to do exactly.