title: how to use AutobahnJs to send a message to a specified client?
body: <p>I need a scheme of push message server.</p>
  
  <p>By now I choose AutobahnJs + AutobahnPython scheme.</p>
  
  <p>use websocket of html5 by AutobahnJs Library connect to server which use by AutobahnPython</p>
  
  <p>now, clientA ,clientB,clientC connect to server. </p>
  
  <p>APPS want to send a message to clientA. How to do it?</p>
  
  <p>this is my flow:
  APPS disguised as a clientD to connect to server.</p>
  
  <p>in javascript, use subscribe channel, every client use the same subscribe channel. 
  clientD publish a message to channel(the same to subscribe channel), the server messaging to all client who subscribe this channel.</p>
  
  <p>Here is a problem, I need APPS(clientD) to send a message to clientA only, not every client who subscribe.how to do this?</p>
  
  <p>Maybe my flow is incorrect. any help and more scheme?</p>