title: spring cloud gateway routes data from inside server to outside client
body: <p>A normal usage scenario is an outside client sends data to inside service through spring cloud gateway. How about the other way round, how to make inside service send request to client through spring cloud gateway too? For example:</p>
  
  <ol>
  <li>client sends request to service (through gateway)</li>
  <li>service answers "request received".</li>
  <li>when service job finishes, sends results to client (I hope it goes through gateway too)</li>
  <li>client answers.</li>
  </ol>
  
  <p>I thought <code>feign</code> could somehow achieve this, but based on materials I found, it needs to be configured with outside URLs statically. Maybe <code>spring-cloud-gateway</code> by nature supports this and I missed reading something?</p>