Ssl – Redirect SSL requests from proxy Apache server to another Apache server

We have a legacy application with URL https://www2.devDocApp.com/ which is running on Ubuntu8 and apache2.2 with no TLS 1.2 support, we had hardtime upgrading apache2.2 and openSSL on Ubuntu 8 box, so now we are standing proxy apache server (secure-devDocApp windows 2012 VM with Apache/2.4.29 (Win64)) which redirects all the requests to https://www2.devDocApp.com/

Below is the apache configuration I've used to set up proxy server secure-devDocApp

<VirtualHost *:443>
Header always set Strict-Transport-Security "max-age=63072000; includeSubdomains; preload" 
DocumentRoot "C:/apache/htdocs"
ServerName  secure-devDocApp    
SSLEngine on
RC4 !aNULL !eNULL !LOW !3DES !MD5 !EXP !PSK !SRP !DSS"


SSLProtocol -ALL TLSv1.2
SSLCertificateFile "C:/apache/conf/server.cer"
SSLCertificateKeyFile "C:/apache/conf/server.key"   
SSLCACertificateFile "C:/apache/conf/ca.cer"
SSLVerifyClient optional
SSLVerifyDepth  3

<FilesMatch "\.(cgi|shtml|phtml|php)$">
    SSLOptions +StdEnvVars
</FilesMatch>
<Directory "C:/apache/cgi-bin">
    SSLOptions +StdEnvVars
</Directory>

ProxyRequests Off
<Proxy *>
Order deny,allow
Allow from all
</Proxy>    
ProxyPass   / https://www2.devDocApp.com/   
SSLProxyEngine on

RequestHeader set X_SSL_CLIENT_M_SERIAL "%{SSL_CLIENT_M_SERIAL}s"
RequestHeader set X_FORWARDED_PROTO "https" env=HTTPS
RequestHeader set SslSubject "%{SSL_CLIENT_S_DN}s"

</VirtualHost>

We have a page '/clientAuth' which requires client certificate authentication, so When am hitting the proxy apache URL https://secure-devDocApp/clientAuth in browser it is prompting to choose from an existing client certificates, but when I choose the client certificate am getting a 404 instead of authorized content, however client certificate authentication works fine on the legacy URL https://www2.devDocApp.com/clientAuth` which prompts for client certificate and I can see the authorized page for the chosen client certificate.

I suspect proxy apache server secure-devDocApp is not forwarding the SSL certificate requests to the legacy apache server of www2.devDocApp.com. Can someone please help me forwarding SSL requests from one apache server to another?