Controlled internet access

Hi, I was wondering if anyone can help. I currently have a setup at work in our accommodation blocks to allows users to access internet via wireless. I have users connecting to wifi routers, which currently ends up going through a transparent squid proxy. User's currently pay me for access to service where I will add there MAC access to access points, but this is alot of work. Is there a way I can control access to internet using my ubuntu squid proxy? E.g. user issued a password/key and once entred user has net access, so no key no internet. Any help would be could, and as a newbie to linux the clear it is, the better.

Can you not use a different

Can you not use a different proxy that allows you to do this?