title: Enable underscores in headers on Azure ingress
body: <p>I have a problem with headers not forwarded into my services, I am not sure how support for Ingress was added, however I have the following Ingress service:</p>
  
  <pre><code>apiVersion: extensions/v1beta1
  kind: Ingress
  metadata:
    name: my-ingress
    annotations:
      ingress.kubernetes.io/rewrite-target: /
      "nginx.org/proxy-pass-headers": "custom_header"
  spec:
    rules:
    - host: myingress.westus.cloudapp.azure.com
      http:
        paths:
        - path: /service1
          backend:
            serviceName: service1
            servicePort: 8080
  </code></pre>
  
  <p>However, my custom_header will not be forwarded. In nginx I set underscores_in_headers:</p>
  
  <pre><code>underscores_in_headers on;
  </code></pre>
  
  <p>How can I add this configuration into my ingress nginx service?</p>
  
  <p>Thanks.</p>