Facebook Connect API Work Flow behind the scene

I have visited a site . I have observed that When I am not logged in Facebook it ask for connect to facebook to download file. After that I hav开发者_Go百科e authenticated their Application. Now Whenever I logging in to Facebook and open this site it automatically detect that I am login in Facebook without any authentication.

I want to know that how it can identify that I am logged in Facebook? Can anybody suggest any good artical which shows the workflow of FaceBook conntect authetication behind the scene?

Authorization and Authentication. Slideshare shares login state with facebook.com via the session cookie on your browser.

The Facebook JavaScript SDK allows your users to register and sign-in to your site using their Facebook accounts. This is done by sharing the logged in user state between http://www.facebook.com/ and your site. A Facebook user remains logged in to your site as long as they are logged in to Facebook and there is a valid access token for your app.