Facebook get user id on page tab (signed_request)

Question

Hello, i've run into a problem.

I have custom page tab, and current user viewing on it. I ask user to grant extended permissions to his profile (using Facebook.showPermissionDialog). If he grants permissions, theoretically, i would have access to the Graph API and other stuff. But when i parse new signed_request param from Facebook, i get oauth_token, bound to current page tab, not to user profile. In other words request to Graph API method 'me' gives me my custom page profile. And I want to get user's profile! How should i get access to it?

How to get access to user's Graph API on Facebook tab?

Answer 1

Tab is much more limited than a regular app. It doesn't know who is visiting it unless they interact with the tab. Basically it was made to emphasize that a tab is designed to be useful to a user who installed it, not to visitors. From docs:

• It doesn't know who the viewing user is when the user first visits the tab. Facebook sends the fb_sig_user and fb_sig_profile_user parameters, both containing the profile owner's user ID.
• If a viewing user interacts with the tab (like submits a form, takes an action that causes an AJAX load of new content, or follows a relative URL that loads on the tab), that user's UID is sent to the application as the fb_sig_user parameter, the profile owner's user ID is sent as the fb_sig_profile_user parameter. The viewing user's session key is key is sent only if the user authorized the application.
• Applications use the owner's session key on the owner's application tabs.

Answer 2

I've figured out how it works. After the user grants permissions, Facebook sends signed_request of current user (and his ID as well), when calling page on my server via Ajax. When the page loads statically - you get signed_request of page tab. Hope it will help somebody.