title: OAuth token types and refreshing
body: <p>In the <a href="https://developers.google.com/accounts/docs/CrossClientAuth" rel="nofollow">Cross-client Identity</a> article by Google it's recommended to store OAuth refresh tokens on the server side.  <br>In the end of the article there is a sentence: </p>
  
  <blockquote>
    <p>Also, if the app always requested a refresh token without checking whether
    the server already had one, this would eventually exhaust the finite
    number of refresh tokens that can be outstanding for a user/app
    combination</p>
  </blockquote>
  
  <p>So I've got 2 questions:<br>
  1) Does it apply to <a href="https://developers.google.com/accounts/docs/CrossClientAuth#androidIdTokens" rel="nofollow">Android ID tokens</a> and so should I save them in Android rather than calling <code>GoogleAuthUtil.getToken()</code> for every sync-with-server session? <p>
  2) How many types of OAuth tokens exist? Only in the mentioned article there are <code>ID token</code>, <code>access token</code> and <code>refresh token</code>. Is there somewhat like a summary on token types?
  <p>
  Thanks!</p>