title: gapi.auth.signOut(); doesn't sign out
body: <p>I have been using Google plus authentication in a development app for some time.</p>
  
  <p>I am aware that it is not supposed to work from localhost, but I am experiencing some really erratic behaviour at the moment.</p>
  
  <p>Sign-in is working as expected on any platform, but signOut (gapi.auth.signOut();) behaves differently on different platforms:</p>
  
  <ol>
  <li>In Firefox on localhost, signOut works as I expect. I click my signOut button, the callback fires and I am logged out.</li>
  <li>In Chrome in-cognito on localhost, when I click my signout button, the callback fires, I am logged out and then immediately logged back in again. This is what I have learned to expect in Chrome/localhost.</li>
  <li>In Chrome (ex-cognito) and any browser on the remote server, the callback function is simply not fired. I have put comments before and after 'gapi.auth.signOut();' and both comments appear in the console, but nothing else happens.</li>
  </ol>
  
  <p>My app is using AngularJS, served from a Node.js/Express server. I am using page-level tags for clientId and scope:</p>
  
  <pre><code>&lt;meta name="google-signin-clientid" content="&lt;%= googleClientId %&gt;" /&gt;
  &lt;meta name="google-signin-scope" content="&lt;%= googleScopes %&gt;" /&gt;
  </code></pre>
  
  <p>and data-attributes for other stuff:</p>
  
  <pre><code>&lt;span class='g-signin' 
    data-approvalprompt='auto' 
    data-redirecturi='postmessage' 
    data-accesstype='offline' 
    data-cookiepolicy='single_host_origin' 
    data-width='wide' 
    data-callback='signinCallback'&gt;
  &lt;/span&gt;
  </code></pre>
  
  <p>I am now at a loss to understand what is going wrong.</p>
  
  <p>Any suggestions gratefully received.</p>