title: How to get some user Information when user buy some items on Apple In app purchase by swift?
body: <p>I am working an app that has In app purchase function.
  And i need some unique user information when they make some purchases in order to store it on my Database for some reason.</p>
  
  <p>So how can i get some info like email,username or userId from the purchased user?</p>
  
  <p>Thanks!  </p>