title: Add active connections to channel when it's created
body: <p>I am trying to prevent who can see events for a particular page, so I am determining and storing the ids of which users have access to a particular page. In channels.js, I can add users to the new page-level channel in app.on('connection') by iterating through the pages like this: app.channel('page-' + pageId).join(connection)</p>
  
  <p>The problem is that a user doesn't start getting broadcasts from that page until after they refresh the browser and re-connect. </p>
  
  <p>What I want to happen is have all connections for a an allowed user start getting broadcasts when the page is created. Is there a way to do that in channels.js, or can I tell it who to start broadcasting to in a hook for the page creation?</p>
  
  <p><em>Editing to add the last thing I tried. "Users-pages" is an associative entity that links Users and Pages.</em></p>
  
  <pre><code>app.service('users-pages').on('created', userPage =&gt; {
      const { connections } = app.channel(app.channels).filter(connection =&gt;
        connection.user.id === userPage.userId
      )
      app.channel('page-' + userPage.pageId).join(connections)
  })
  </code></pre>