We're trying to implement a subscription service with in-app purchase in our app. The problem is our service does not require a user account for the past year of service. Users simply use this service with advertisements shown. We want to give them a subscription where they can buy for say, 3 months to have the advertisement removed.

How can this be done? We'll have to make it a consumable because it is a subscription. But we wouldn't know when the subscription end.

• We can't save the state locally because the user might reinstall the app
• We can't save the state on the server and tie it to their device because sometimes the user changes device
• We don't have a user account to tie the subscription to and we don't want to introduce a user account system which spoils the experience.

Is there some way of associating the purchase with their iTunes account? So that it is carried with them when they reinstall or changes device?