title: How to avoid a 502.3 error (due to unknown HTTP header) when web app is behind a reverse proxy?
body: <p>[Apologies for the poorly phrased question]</p>
  
  <p>Here's my situation: -</p>
  
  <p>I have a web app  that inserts a custom HTTP header in its response (the header value just emits some debug performance information that was useful to me during development - it should probably never had gone out but I left it in because it was very small and I <em>thought</em> it would have minimal impact).</p>
  
  <p>However this innocuous change has had a pretty dramatic effect when we try and host the app behind a reverse proxy.  When using IIS + ARR + Url Rewrite as the reverse proxy, all responses come back with the status code 502.3 Bad Gateway.</p>
  
  <p>The fix is to obviously remove the header - but that would mean a re-compile.  </p>
  
  <p>Is there a way to configure either the proxy or the site behind the proxy t get around this issue?</p>