title: Deepstream.io - Server callback when client disconnects?
body: <p>I'm building a Multiplayer game with Deepstream using an Authorative server model. My server is just another Node.JS client. Is there any way for my server to find out if any of the connected clients disconnected or closed their connection? Is there an event or a callback that is exposed?</p>
  
  <p>I can build a heartbeat system but I wonder if this can be avoided.</p>