title: Google Calendar API v3 - get calendarId (email) from OAuth token object
body: <p>How to get calendarId (user's email) from OAuth token object?</p>
  
  <p>Details: Using the Google Javascript Client Library. 
  After authorization, I need to get the user's email, which is the calendarId from the token object. </p>
  
  <p>For Google Plus, the docs say that 'me' keyword can be used to refer to current authenticated user. It doesn't work for Calendar API. 
  What should I do for calendar API?</p>
  
  <p>Please help</p>