What is a long-term method I can use to uniquely identify an iOS device?

Question

What is the best way to uniquely register an iOS Device, which won\'t be limited by future Apple restrictions?

My current approach to register an iOS device (basical

Answer 1

Unless your application is for managing my Apple devices, it is the wrong approach. As a user, I don't want you to know which device I'm using. I want you to recognize me, whatever the device I use. I want to be able to replace a defective device. Apple will restrict more and more the access to this information.

[edit] I can't see how a MAC address could work. My iOS devices can have multiple.