title: Configure Apache to send SSL Client certificate to backend server
body: <p>i want to configure Apache so that it receives a client certificate, an passes it to another server.
  I'm using:</p>
  
  <ul>
  <li>apache 2.0.65 on windows</li>
  <li>the backend server is an apache-based solution (IBM HTTP Server)</li>
  </ul>
  
  <p>I tried this config:</p>
  
  <pre><code>&lt;VirtualHost *:443&gt;
  ServerName apacheserver.domain.com
  SSLEngine on
  SSLProxyEngine on
  SSLCertificateFile "e:/Apache/Apache2/conf/server.cer"
  SSLCertificateKeyFile "e:/Apache/Apache2/conf/server.key"
  SSLCACertificateFile  "e:/Apache/Apache2/conf/certca.cer"
  SSLVerifyClient require
  SSLVerifyDepth 2
  ProxyPreserveHost on
  ProxyRequests off
  &lt;Proxy *&gt;
    AddDefaultCharset Off
    Order deny,allow
    Allow from all
  &lt;/Proxy&gt;
  # initialize the special headers to a blank value to avoid http header forgeries
  RequestHeader set SSL_CLIENT_S_DN    ""
  RequestHeader set SSL_CLIENT_I_DN    ""
  RequestHeader set SSL_SERVER_S_DN_OU ""
  RequestHeader set SSL_CLIENT_VERIFY  ""
  &lt;Directory /&gt;
    # add all the SSL_* you need in the internal web application
    RequestHeader set SSL_CLIENT_S_DN "%{SSL_CLIENT_S_DN}e"
    RequestHeader set SSL_CLIENT_I_DN "%{SSL_CLIENT_I_DN}e"
    RequestHeader set SSL_SERVER_S_DN_OU "%{SSL_SERVER_S_DN_OU}e"
    RequestHeader set SSL_CLIENT_VERIFY "%{SSL_CLIENT_VERIFY}e"
    ProxyPass  https://192.168.10.191/
    ProxyPassReverse  https://192.168.10.191/
  &lt;/Directory&gt;
  &lt;/VirtualHost&gt;
  </code></pre>
  
  <p>when i try this config, i have this error on the error.log file of apache:</p>
  
  <pre><code>[Tue Dec 31 12:14:52 2013] [warn] Proxy client certificate callback: (apacheserver.domain.com:443) downstream server wanted client certificate but none are configured
  </code></pre>
  
  <p>any ideas? </p>