title: how to properly check expiration time of renewable in app subscription in ios
body: <p>i'm developing application with in app subscriptions (monthly, yearly). When i'm getting the receipt from apple with response (i'm validating receipt with apple server, i know this is not a good idea, but still), i want to check the expiration date of the subscription. Here's the checking part.</p>
  
  <pre><code>NSDate *currentDate = [NSDate date];
  NSDate *expireDate = receipt[@"expires_date"];
  NSComparisonResult result = [currentDate compare:expireDate];
  BOOL subscribed = (result != NSOrderedDescending);
  </code></pre>
  
  <p>But if the device time is wrong(the user changed the time of the device) how can i be sure that subscription is still active ? Maybe i should request the current time from the server ? </p>