Switching from a paid app to a free app with auto-renewing subscription

I have an app which costs $5. I'd like to change this so that the app is free and that users must purchase an auto-renewing subscription to use it. I know how to implement the auto-renewing subscription, but the problem is dealing with users who have already bought the app for $5; I'd like to continue letting these users use my app without a subscription.

The rub is that for privacy reasons I can't store any identifying information on my server which link an account for my app to a specific person (not even UIDID). What I can do is maintain a separate database table which links UIDIDs to subscription purchase receipts which will allow me to know if a user has a subscription.

So my question is, how can I identify users who got my app when it cost $5? I know there's a way to restore in-app purchase receipts, but is there a way to to retrieve a receipt for the initial purchase of the $5 app which I could store on my server?

The poor man's solution is just to mark all current UIDID开发者_如何学Pythons (i.e. the UIDIDs of people who have paid $5) in my server as paid, but then they would have to buy a subscription if they ever wanted to use my app from a different device.

The previously selected answer is outdated. The new answer is that it is possible today with the new receipts that were standardized this year (2013).

The receipt now has two additional fields: original_application_version and original_purchase_date which can be used to detect when a user purchased and therefore be used to guide logic around what users should get what features.

You can see more about 10 minutes in here: http://devstreaming.apple.com/videos/wwdc/2013/308xex4x6ybggtlw4ztv0sg5btp/308/308-SD.mov?dl=1 or if that link dies here: https://developer.apple.com/wwdc/videos/ and search for Using Receipts to Protect Your Digital Sales.

Chaning your business model like this is not very well supported by the App Store.

Your "poor mans" solution is probably one of the best of a poor set of options.

Another one would be to switch to a new app entirely (just a different bundle ID in practice). Anyone using your old app would have paid, regardless of which device they use. Anyone using the "new" app would need a subscription. Obviously you'd lose any reviews and possibly external links that you currently have.