I am not a full-fledged Facebook app developer. Recently working on a website that will use Facebook login for user authentication. I am using the CakePHP framework to build the website.
When I create a new app on the Facebook developer page, I noticed that my newly created app is using Graph API v2.0 instead of v1.0. I found this when I saw Facebook, after authorization my app, gave me the user_id of the Facebook user which was something different than the original user_id. Then I discovered Facebook is hiding the actual user_id and giving us app_scoped_user_id instead. This id is app-specific meaning that the same user has a different app_scoped_user_id in a different Facebook app. So there is no way to get the actual Facebook user id anymore.
Facebook released Graph API v2.0 which has lots of things to look at. These include Facebook login, permission, dialog, etc. Here is the upgrade guide from v1.0 to v2.0. Also, look here for permissions for Facebook login. Don’t forget to look at the best practice guideline for Facebook login.