title: How to detect if user cancel auto-renewable subscriptions during the free trial period?
body: <p>Apple's document does not seem to mention this.  So if user cancels an auto-renewable subscription purchased during the free trial period, how do we detect?</p>
  
  <p>In appstore receipt JSON there is this field: <code>is_trial_period</code>.  But I think this is for indication of whether the free trial period is over.</p>
  
  <p>The only thing I can think of is this <code>NSBundle.mainBundle().appStoreReceiptURL?.path</code>  and if this is nil than that will indicate the user has not subscribed or cancel within the free trial period.  But for sandbox testing, there is no way to do a cancel during free trial period to test this scenario.</p>
  
  <p>Does anyone have a solid knowledge of this?</p>