https://github.com/facebook/facebook-php-sdk
Facebook PHP SDK (v.3.2.2)
The Facebook Platform is a set of APIs that make your app more social.
This repository contains the open source PHP SDK that allows you to access Facebook Platform from your PHP app. Except as otherwise noted, the Facebook PHP SDK is licensed under the Apache Licence, Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0.html).
On your page, you should either check if the user already allowed the application access, using FB::instance()->getUser(). This can be either in an AJAX call or your controller.
If FB::instance()->getUser() returns false, you should either redirect or popup the permission dialog pointing to FB::instance()->getLoginUrl().
The callback URL is facebook/auth by default, that issues FB::instance()->getUser() and FB::instance->getAccessToken() so you can use the user app data right away.
Then issue your OpenGraph calls using FB::instance()->get(''). If you want to extend the FB class, extend Core_FB.