title: Nginx proxy_ssl_certificate not working as expected
body: <p>I'm using nginx as a proxy to a backend server. 
  The backend server is also using nginx and enforcing client certificate authentication using the <code>ssl_client_certificate</code> and <code>ssl_verify_client</code> directives.</p>
  
  <p>In my nginx server I set the following:</p>
  
  <pre><code>location  /proxy {
      proxy_pass             https://www.backend.com;
  
      proxy_set_header       X-Forwarded-Host $host;
      proxy_set_header       X-Forwarded-Server $host;
      proxy_set_header       X-Forwarded-For $proxy_add_x_forwarded_for;
  
      proxy_ssl_certificate      /etc/nginx/cert/client.crt;
      proxy_ssl_certificate_key  /etc/nginx/cert/client.key;
  }
  </code></pre>
  
  <p>according to <a href="http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_ssl_certificate">the nginx docs</a>.</p>
  
  <p>However, the backend is still responding with a 400 reponse code <code>"No required SSL certificate was sent"</code>.</p>
  
  <p>Note that when issuing requests to the backend server using wget with the client certificate, I get a valid 200 OK response:</p>
  
  <pre><code>wget --certificate=/etc/nginx/cert/client.crt --private-key=/etc/nginx/cert/client.key https://www.backend.com
  </code></pre>
  
  <p>What am I missing in my nginx configuration?</p>