Not sure if it will help but here is my proxy pass configuration:
<IfModule mod_ssl.c>
<VirtualHost _default_:443>
ServerAdmin webmaster@localhost
DocumentRoot /var/www
SSLEngine on
SSLProtocol all -SSLv2
SSLCipherSuite ALL:!ADH:!EXPORT:!SSLv2:RC4+RSA:+HIGH:+MEDIUM
SSLCertificateFile /etc/apache2/ssl/ssl.crt
SSLCertificateKeyFile /etc/apache2/ssl/ssl.key
SSLCACertificateFile /etc/apache2/ssl/ca.pem
ProxyRequests Off
ProxyPreserveHost Off
AllowEncodedSlashes On
KeepAlive Off
<Location /os/>
AuthType Basic
AuthName "Restricted"
AuthUserFile /etc/apache2/.htpasswd
AuthBasicProvider file
Require user admin
ProxyPass http://10.0.2.23/ timeout=1200 KeepAlive=On
ProxyPassReverse http://10.0.2.23/
<IfModule mod_headers.c>
Header set Access-Control-Allow-Origin "*"
</IfModule>
</Location>
</VirtualHost>
</IfModule>
This allows me to access the device using: https://my.domain.com/os and also uses Basic authentication. You can try to fit that into your configuration and see if it helps.