title: How to support multiple devices with non-renewing In-App Purchase?
body: <p>I'm building an iOS app that will include an IAP with a non-renewing subscription. Apple provides this nugget in their <a href="https://developer.apple.com/library/ios/#documentation/NetworkingInternet/Conceptual/StoreKitGuide/APIOverview/OverviewoftheStoreKitAPI.html" rel="nofollow noreferrer">overview of IAP</a>:</p>
  
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      <p>You are required to deliver non-renewing subscriptions to all devices owned by the user. Non-renewing subscriptions are not automatically synchronized to all devices by Store Kit; you must implement this infrastructure yourself. For example, most subscriptions are provided by an external server; your server would need to implement a mechanism to identify users and associate subscription purchases with the user who purchased them.</p>
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  <p>I would like to follow this rule: I want my users to be able to take advantage of the subscription they purchase on one device on other devices as well. So how can I identify the same user across their iPhone and iPad? I understand that you can't use the Apple ID, and you can't rely on a registration method.</p>
  
  <p>I just now found <a href="https://stackoverflow.com/questions/9466392/app-rejected-how-to-track-user-non-renewing-subscription">this question</a>; the answer given there doesn't appear to be workable. There must be something more elegant that others have done.</p>