问题
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 being run in. How specifically does FB SSO accomplish this? (How does it know which app to reopen after the permissions are granted?)
We are building a SDK that interacts with Facebook, and it is not clear how the facebook app figures out which app to return to.
回答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/
来源：https://stackoverflow.com/questions/10953229/how-does-facebook-sso-know-which-app-to-return-to