Nós temos uma configuração similar e estamos usando isso (é claro que você precisa carregar antes mod_proxy, mod_ssl e mod_proy_http):
ProxyRequests Off
# SSLProxyEngine On # only required if the proxied service would be HTTPS as well
# Meaning if we would reverse proxy https://thirdparty.com/app/
# Thanks @Piskvor for the clarification.
<Proxy *>
Order deny,allow
Allow from all
</Proxy>
ProxyPass /proxy/ http://thirdparty.com/app/
ProxyPassReverse /proxy/ http://thirdparty.com/app/
<Location /proxy/>
ProxyPassReverse /
Order deny,allow
Allow from all
</Location>
Header edit Location ^http://thirdparty.com/app/ https://thirdparty.com/app/