Question On Sessions Cdbhttpsession

Hi, I've been trying to locate where the CDbHttpSession is called after login, to rewrite it.

My problem is that I have 3 products in my App, and each are restricted on X simultaneous users, so I shouldn't allow any user to access these products until someone closes session or the admin manually removes the session from the DB.

Any help on how could I achieve it?

Thanks!