title: nginx custom header validation
body: <p>I and trying to evaluate a header value for certain locations. Something like this:</p>
  
  <pre><code>location /risksecretspoc {
      set my_header $http_MY_CUSTOM_HEADER;
      if($my_header != 'some-value') {
          return 403;
      }
      proxy_set_header    Host riskservicesdev.mydomain.co.za;
      proxy_pass          https://rsk-generic-dev.mydomain.co.za;
  }
  </code></pre>
  
  <p>The error I'm getting is: 
  nginx: [emerg] invalid variable name "my_header" in /etc/nginx/nginx_default.conf:17</p>