[eluser]InsiteFX[/eluser]
In your auth library constructor check to see if they are login if not then log them in as a visitor like a dummy login, then add the vistor to the visitors_online table.
If they are a user then log them in and add them to the users_online table.
You will also need to check for banned users on your login.
When a visitor logs out and leaves you need to delete them from the visitors_online table also when a user logs out you need to delete them form the users_online table.
I am writing a new auth system that will be using all of this now...
InsiteFX