title: Fastify & NestJS - How to set response headers in interceptor
body: <p>I'm trying to set the response headers in my interceptor, and have had no luck with any method I've found yet. I've tried:</p>
  
  <pre><code> const request = context.switchToHttp().getRequest();
   const response = context.switchToHttp().getResponse();
   &lt;snippet of code from below&gt;
   return next.handle();
  </code></pre>
  
  <ul>
  <li><code>request.res.headers['my-header'] = 'xyz'</code></li>
  <li><code>response.header('my-header', 'xyz')</code></li>
  <li><code>response.headers['my-header'] = 'xyz'</code></li>
  <li><code>response.header['my-header'] = 'xyz'</code></li>
  </ul>
  
  <p>with no luck. The first option says that res is undefined, the second "Cannot read property 'Symbol(fastify.reply.headers)' of undefined", and the others just do nothing.</p>