To test your re-login flow when your app's access to people's data has expired, FB Login provides the ability to set a custom expiration period for test user data access.
Now, when you log in as this test user, access to your data expires after the number of minutes you entered in the Login Expiration Time dialog box.
When access to someone's data has expired, they must renew consent for login by tapping the Continue with Facebook button, and they must agree to permissions again.