title: iOS In-App purchase subscriptions integration with a third party system
body: <p>I need to build an app for a system, which already has a subscription on its website. It looks like Apple doesn't allow to use any own subscriptions and forces to integrate any app with iOS in-app subscriptions.</p>
  
  <p>Is it any way to integrate two subscription systems? The main problem is that users can manage iOS subscriptions via iTunes and I can't find whether it's possible to get information about this and to stop subscription in the existing system if it's stopped via iTunes.</p>
  
  <p>So is it possible to get notifications about unsubscribed iTunes users?</p>