title: detect host/ip of another site which use js to make requests to my rails app
body: <p>I have a js-script (client-side) on site <code>A</code> which makes requests to my rails app (site <code>B</code>).</p>
  
  <p>When this request occurs, how can site <code>B</code> detect host/ip of site <code>A</code>?</p>