code: private void fireTunnelClosedEvent(AuthenticatedUser authenticatedUser,
              Credentials credentials, GuacamoleTunnel tunnel)
              throws GuacamoleException {
          listenerService.handleEvent(new TunnelCloseEvent(authenticatedUser,
                  credentials, tunnel));
      }
docs: Notifies bound listeners that a tunnel is to be closed.
  Listeners are allowed to veto a request to close a tunnel by throwing any
  GuacamoleException.
  
  @param authenticatedUser
  The AuthenticatedUser associated with the user for whom the tunnel
  is being closed.
  
  @param credentials
  Credentials that authenticate the user.
  
  @param tunnel
  The tunnel that was connected.
  
  @throws GuacamoleException
  If thrown by a listener.