title: Can I extend the users current auto-renewable subscription expiration date
body: <p>I would like to implement a referral feature in an app that would add days to the user's current active subscription. Is there a way to do that using Apple's auto-renewable subscriptions?</p>
  <p>Example</p>
  <ul>
  <li>A user has a 12-month subscription that will renew in 3 months for an additional 12 months</li>
  <li>The user refers a friend to use the app</li>
  </ul>
  <p>Expected result</p>
  <ul>
  <li>The user has a 12-month subscription that will renew in 4 months for an additional 12 months</li>
  </ul>