code: @Handler
      public void onProtocolSwitchAccepted(
              ProtocolSwitchAccepted event, WebAppMsgChannel appChannel) {
          appChannel.handleProtocolSwitchAccepted(event, appChannel);
      }
docs: Send the response indicating that the protocol switch was accepted
  and causes subsequent data to be handled as {@link Input} and
  {@link Output} events on the channel.
  
  As a convenience, the channel is associates with the URI that
  was used to request the protocol switch using {@link URI} as key.
  
  @param event the event
  @param appChannel the channel