Subscribing to a Backplane channel and testing type, then sending the messageURL to a server.

backplane_subscribe_switch_send.js

(function() {
  if (typeof window.Backplane !== 'function' || parseInt(Backplane.version) !== 2)
    return;
 
  /**
   * Callback function to be executed on BP ready
   */
  function bp_ready_callback() {
    Backplane.subscribe(function(message){
      switch(message.type) {
        case 'identity/login':
          // Pass via JSONP to an endpoint "url"
          var script = document.createElement('script');
          script.type = "text/javascript";
          script.src = url
            + "&bp_message=" + encodeURIComponent(message.messageURL);
          document.getElementsByTagName('HEAD')[0].appendChild(script);
          break;
        default:
          // Don't do anything if this isn't a type we recognize
      }
    }
  }
 
  // Pass in function from above
  Backplane(bp_ready_callback);
})();