I'm wondering how to make an authentication screen (in this case with a 4-digit code) which would open every time the app is opened. I achieved this in a previous iOS project by showing a modal window from the AppDelegate, and I was wondering what the best way to go about doing this would be on Android. I can't seen to find info about this specific case anywhere.
Is there some kind of equivalent to the AppDelegate in Android? And how can I prevent users from just skipping the screen by clicking the android default back button?