You can completely replace the registration process as long as the application doesn't need any data from the user. If the app needs data then you can pre-fill

You can completely replace the registration process as long as the application doesn't need any data from the user. If the app needs data then you can pre-fill it (as we do at Clickpass). Even pre-filled though you still need to confirm with the user that they're happy to send it (you can't allow an app to call any data it wants from a user without asking them first)