title: Detecting a cancelled itunes login alert for in-app purchases
body: <p>I have a class that implements <code>SKPaymentTransactionObserver</code>. However when clicking a buy button, if the user is not signed into the app store they get an alert asking for an existing ID or to create a new one. If the use clicks cancel from this, or a subsequent login credentials alert, I receive no notification of that cancellation. I have an activity view covering the screen after the buy button is clicked so I really need to know if the login alert was cancelled.</p>
  
  <p>I already test for the error code <code>SKErrorPaymentCancelled</code> and that works if the purchase process is cancelled after logging in. I'm testing on a device.</p>
  
  <p>Any clues?</p>
  
  <p>-UPDATE- </p>
  
  <p>Apologies I forgot to mention that this only happened when attempting to restore transactions, and that reveals the answer: my lack of knowledge about the protocol.</p>