How does Facebook SSO know which app to return to?

Question

Using Facebook SSO (Single Sign on), after the system prompts the user for permissions to work with their Facebook account, it directs the user back to the app that SSO was bein

Answer 1

When you add the Facebook SDK, one of the steps is to register a URL scheme for your app with your API key.

When you authorize the app in Facebook it tries to open the URL (usually formatted like fbXXXXXXXXXXX) and since your app is set to handle this URL scheme so the app is opened.

And here's a list of other apps you can communicate using handleOpenURL:

http://handleopenurl.com/