docs: protected void doFilterImpl(ServletRequest pRequest, ServletResponse pResponse, FilterChain pChain) throws IOException, ServletException {
          // NOTE: super invokes trigger() and image specific doFilter() if needed
          super.doFilterImpl(pRequest, pResponse, pChain);
  
          if (pResponse instanceof HttpServletResponse) {
              // Update the Vary HTTP header field
              ((HttpServletResponse) pResponse).addHeader(HTTP_HEADER_VARY, HTTP_HEADER_ACCEPT);
              //((HttpServletResponse) pResponse).addHeader(HTTP_HEADER_VARY, HTTP_HEADER_USER_AGENT);
          }
      }