Unique identifier for an iPhone app, NOT device

I want to avoid user registration in my app, and to identity my user by purchased app. If someone purchase app on his iPhone, and with the same Apple ID download this app on other device, I want to use the same settings and content on this devices.

Is posible to use identifiers like AppleID (without entering in input field开发者_运维技巧 by user)?

I found similar question but UniqueIdentifier is unique only for physical device, not for user.

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No. Apple does not give an app access to the user's Apple ID without the user's involvement. And for good reason.

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I don't think you should outsmart the user. You can't assert that the user will want the same settings on another device. For instance I manage all my family iphones and download apps for them, all of them have their own accounts in apps and like different preferences. That's why it's the best to allow users to create accounts and sing in. This way user has a clear understanding what he/she is doing.