title: SignalR get groups user is in
body: <p>I'm  making a 1-to-1 chat application and I'm using groups for that.</p>
  
  <p>You join a group with <code>Groups.Add(Context.ConnectionId, roomName)</code>.</p>
  
  <p>And whenever a message is sent, I want to call</p>
  
  <pre><code>Clients.Group(roomName).addMessage(username, text);
  </code></pre>
  
  <p>But for that I need a <code>roomName</code> variable. How do I retrieve the rooms an user joined?</p>