I have an Ubuntu server acting as a firewall/gateway to a lan consisting of 30 PC's.
Of these PC's, only some may access the internet.

I now need to allow a single PC to access the internet, but I need to be able to block certain websites such as twitter.com and Facebook and some others (as its proving to be counter-productive).

On the Ubuntu server, I have squid running (not transparent) that allows PC's to browse the net after authenticating.

After setting up some rules in squid, I'm finding that its not blocking the sites I've designated.

Also, how does https factor into this?

Before I post configs and logs and whatnot, I'd like to just get someone's opinion as to whether I'm going about it the right way. Maybe someone can tell me in general how it should be accomplished?

Thanks in advance.