The assumptions you usually have to make with that approach is: - The app is used on one device - Only one user has access to a device - There is a convenien

The assumptions you usually have to make with that approach is: - The app is used on one device - Only one user has access to a device - There is a convenient or reliable way to identify a device for all platforms you target Plenty of apps can live with those, and plenty can't. email address is one of the least bad ways to do it.