title: iOS: How to detect if a user is subscribed to an auto-renewable subscription
body: <p>Hopefully the title is self-explanatory. I'm trying to do something like this:</p>
  
  <pre><code>checkIfUserIsSubscribedToProduct(productID, transactionID: "some-unique-transaction-string", completion: { error, status in
      if error == nil {
          if status ==  .Subscribed {
              // do something fun
          }
      }
   }
  </code></pre>
  
  <p>does anything like the hypothetical code I've provided exist? I feel like I'm taking crazy pills</p>
  
  <p><strong>Edit</strong></p>
  
  <p>In similar questions I keep seeing a generic answer of "oh you gotta validate the receipt" but no explanation on how, or even what a receipt is. Could someone provide me with how to "validate the receipt"? I tried <a href="https://developer.apple.com/library/ios/releasenotes/General/ValidateAppStoreReceipt/Chapters/ValidateRemotely.html#//apple_ref/doc/uid/TP40010573-CH104-SW1">this tutorial</a> but didn't seem to work.</p>
  
  <p><strong>Edit - For Bounty</strong></p>
  
  <p>Please address the following situation: A user subscribes to my auto-renewable subscription and gets more digital content because of it - cool, implemented. But how do I check whether that subscription is still valid (i.e. they did not cancel their subscription) each time they open the app? <strong>What is the simplest solution to check this?</strong> Is there something like the hypothetical code I provided in my question? Please walk me through this and provide any further details on the subject that may be helpful.</p>