code: protected void cancel(HttpServletRequest httpRequest, HttpServletResponse httpResponse)
        throws ExternalAuthenticationException, IOException {
      this.error(httpRequest, httpResponse, ExtAuthnEventIds.CANCEL_AUTHN);
    }
docs: Method that should be invoked before exiting the external authentication process and indicate that the user
  cancelled the authentication.
  
  @param httpRequest
  the HTTP request
  @param httpResponse
  the HTTP response
  @throws ExternalAuthenticationException
  for Shibboleth session errors
  @throws IOException
  for IO errors