code: @Override
      public void handleRequest(ServletRequest req, ServletResponse res) throws Exception {
          if (req instanceof HttpServletRequest && res instanceof HttpServletResponse) {
              HttpServletRequest request = (HttpServletRequest) req;
              HttpServletResponse response = (HttpServletResponse) res;
              boolean handleByProvider = handleProviderAuthenticate(request, response);
              if (!handleByProvider) {
                  formLogin(request, response, referrerURLHandler);
              }
          }
      }
docs: {@inheritDoc}