Apple - In app purchase: How to make sure the user is authorised to use Free trial subscription only one time?

Question

I have auto renewable subscription with free trial. What happens if the user cancels the subscription during the trial period, and after a day or a week or a month, he buys the subscription again. Did he get another trial period? If so, how can you prevent it. how to avoid abuse? In Apple's papers - I have not seen a clear reference to this.

Answer 1

Validate the receipt either from the app or from your server:

https://developer.apple.com/library/ios/releasenotes/General/ValidateAppStoreReceipt/Introduction.html

It will tell if the subscription has been cancelled.