Codeigniter and Facebook API expert wanted

I have a site, [login to view URL] built with Codeigniter. Currently, users can register and login. However, I would like to replace the existing register/login with a mechanism where users can register/login with their Facebook accounts instead. Specifically I want the following features: 1. Replace the existing register/login mechanism with one where users can register/login with their Facebook accounts 2. Any necessary Codeigniter (user) session variables are enabled so that the user appears "logged in" as normal, i.e. no loss of functionality. It should be easy enough to see what variables are enabled with the current register/login mechanism. 3. On register only, the user's FB status is updated to show that they have registered with Foodbroo. Thanks Jake