Getting a user's iTunes Connect username?

Question

I'm not looking to harvest information, I'm just trying to create a way to offer my users custom promo codes for In App Purchases since Apple doesn't offer promo codes for IAP. I'm looking for a way to identify a user when they move from device to device so I can unlock their In App Purchases they've gotten access to by using one of my custom promo codes.

Is there anyway to programmatically get the current user's iTunes Connect username?

Answer 1

No, and that is the way it should be. I, as a user, don't want that a developer can get my Apple Id which is also my email address.

The only way I think this works is to let the user create an account on a server which is managed by you.