title: passport-google-oauth unable to logout user
body: <p>I use the <code>passport-google-oauth</code> module to authenticate users on a web application I built using <code>Express.js</code>. The logout event is handled this way:</p>
  
  <pre><code>app.get('/logout', function(req, res) {
      console.log("logged out!");
      req.logout();
      res.redirect('/');
  });
  </code></pre>
  
  <p>While this does redirect the user to the login page (at <code>/</code>), I'm not sure it really logs him out. After clicking on logout, when I open <code>Gmail</code> in a new tab, I remain logged in there (and no, I hadn't logged into <code>Gmail</code> earlier). How can I fix this? Also, what does <code>req.logout()</code> do to log the user out?</p>