Pulling Subject Alt Name - Apache Reverse Proxy PIV CAC Authentication

Question

I have created an apache 2.2 reverse proxy running on red hat.

This proxy will need to accept a client certificate, pull the needed information, and pass that along to an application running locally within the header.

NameVirtualHost *:443
<VirtualHost *:443>
   ServerName SearchHead
   SSLEngine on
   SSLVerifyClient require
   SSLVerifyDepth 5
   SSLCACertificateFile /etc/pki/ca-chain.cert.pem
   ProxyPass / http://127.0.0.1:8000/ retry=0
   ProxyPassReverse / http://127.0.0.1:8000/
   RequestHeader set    SSL_CLIENT_S_DN "%{SSL_CLIENT_S_DN_CN}s"
   RequestHeader edit   SSL_CLIENT_S_DN CN=([^,]+) $1
   <Proxy *>
       AddDefaultCharset off
       Order deny,allow
       Allow from all
   </Proxy>
</VirtualHost>

According to documentation: https://httpd.apache.org/docs/2.2/mod/mod_ssl.html I see nothing that will allow me to pull this. Unfortunately, we cannot support a php based solution, nor anything not supported from the Red Hat Enterprise Linux 6 Repos.

DoD middleware states http://www.cac.mil/docs/DoD-CAC-Middleware-Requirements-Release-4.0_v1.01_16Nov2012.pdf Smart Card Logon (1.3.6.1.4.1.311.20.2.2) which lies in the Subject Alt Name of the certificate.

Any thoughts?