This is to document and share the solution to a problem I faced, hopefully it’s of benefit to others as well.
Problem:
Using the Facebook iOS SDK to perform a Facebook login from my iOS app, it returns to my app immediately from the Facebook app without showing any login screen or dialog box if the user has already granted the requested permissions previously and logged out after that. This behavior is the same whether the login is via the Facebook iOS app or through a webview within the app itself.
This can be a problem especially if your app is trying to support multiple Facebook users, as users may not have already logged in to the correct account in the Facebook app beforehand. By returning to our app immediately without explicitly showing the Facebook account used, users will login with the current account used in Facebook, which could be the wrong account.
This behavior occurs when the “iOS Bundle ID” has been set in the app settings in Facebook https://developers.facebook.com/apps
This is also mentioned in Pro-tip 3 (which I believe was just recently added) of the Facebook Login doc.
In order to avoid this behavior, the “iOS Bundle ID” field needs to be blanked out. And from recent experience, this may involve deleting and creating the whole “Native iOS App” section again, as simply deleting the “iOS Bundle ID” and saving the changes does not appear to have any effect.