Access OMV GUI behind Reverse Proxy (Apache2)

Hallo,

I added the following line to my apache2 config and I can call the page, but I cannot see any login form.

<Location /OMV>
ProxyPass https://xxx.xxx.xxx.xxx:443
ProxyPassReverse https://xxx.xxx.xxx.xxx:443
</Location>

Checked the Chrome console and could find that some css couldn't be found and some variable couldn't be loaded.
What I have to configure, that OMV can run behind a proxy?

Thanks,
Jacek