code: @Override
      protected void doFilter(final HttpServletRequest _request,
                              final HttpServletResponse _response,
                              final FilterChain _chain)
          throws IOException, ServletException
      {
          if (isLoggedIn(_request)) {
              _chain.doFilter(_request, _response);
          } else {
              doAuthenticate(_request, _response, _chain);
          }
      }
docs: If the current user is already logged in, nothing is filtered.
  @param _request      HttpServletRequest
  @param _response     HttpServletResponse
  @param _chain        FilterChain
  @see #doAuthenticate
  @throws IOException on error
  @throws ServletException on error