title: Configure Apache Client Certificate Authentication for proxy
body: <p>I have 3 Backend API servers(HTTPS), API servers have different authorization permissions for different users based on user certificate, I am configuring apache to load balance the 3 backend servers, like below</p>
  
  <pre><code>&lt;VirtualHost *:zzzz&gt;
         SSLEngine on
         SSLCertificateFile /path/to/server.crt
         SSLCertificateKeyFile /path/to/server.key
         SSLCACertificateFile /path/to/ca.crt
         SSLProxyEngine on
         SSLProxyVerify none
         SSLProxyCheckPeerCN off
         SSLProxyCheckPeerName off
         SSLProxyCheckPeerExpire off
         &lt;Proxy balancer://api_server&gt;
             BalancerMember https://xx.xx.xx.xx:yyyy
             BalancerMember https://xx.xx.xx.xx:yyyy
         &lt;/Proxy&gt;
         ProxyPass / balancer://api_server/
  &lt;/VirtualHost&gt;
  </code></pre>
  
  <p>The problem is that when a client request <code>apache</code>, with certificates, only the request goes to the API server, not the certificates, and API server responses unauthorized user, I tried using <code>SSLProxyMachineCertificateFile</code>, but it only accepts one set of certificate, and every time passes the same certificate, but in this case, the authorization happens only based on certificates.</p>
  
  <p>Is there a way to blindly forward HTTPS request to API? or any other suggestions is warmly welcomed.</p>