code: @Override
      public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
          HttpServletResponse response = (HttpServletResponse) res;
          response.setHeader("Access-Control-Allow-Origin", allowOrigin);
          response.setHeader("Access-Control-Allow-Methods", allowMethod);
          response.setHeader("Access-Control-Max-Age", maxAge);
          response.setHeader("Access-Control-Allow-Headers", allowHeaders);
          chain.doFilter(req, res);
      }
docs: Sets the headers to support CORS
  @see javax.servlet.Filter#doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)