title: Socket.io : Get Client sessionID at any point
body: <p>I know how to retrieve the client sessionID when the user connects.</p>
  
  <p>But I'd like to retrieve it at any time, for example when the client clicks on something, I would like to be able to know who clicked, what their sessionID was.</p>
  
  <p><code>socket.sessionID</code> doesn't work, nor does <code>socket.handshake.sessionID</code></p>
  
  <p>For example :</p>
  
  <p>I have this express route :</p>
  
  <pre><code>.get('/result/:survey', function(req, res) {
      res.redirect('/result/'+req.params.survey+'/1');
  })
  </code></pre>
  
  <p>Just before the redirection, I'd like to make the user join a socket room, and also get their sessionID. How could I possibly do that ? According to the doc, it would be <code>socket.join('room')</code> but I doubt <code>socket</code>only represents the connection I have with the client, and not with the other clients. Maybe I'm just having trouble understanding sockets !</p>