How to identify the same user on different iOS Devices

Is it possible to identify the same user on different iOS Devices (sync'd with the same itunes account)?

Our goal is to build an app with an initial use period (like 10 days) followed by an auto-renewable subscription (similar to the The Daily app).

To prevent users from restarting the initial period by reinstalling the app or installing it on another device we are looking for a way to identify the user. If possible even on different devices.

We tested this with the daily app and it recogni开发者_如何学Czed our expired trial period correctly if we installed it on a different device using the same iTunes account.

Does iOS SDK (Store Kit) offer any support to accomplish this or do we have to implement a custom system?

Thanks for any advice.

Best regards,

I might be wrong, but I think if you receive the APN token, that's unique for all devices. ALternatively, you could track the phone's device ID.