Hi.
You can use proxy pass and proxy reverse to solve this
ie
we have two web servers, external, and internal (egroupware)
we use an internall address like
egroupwareserver.mydomain.com/egroupware
and an external address like
mydomain.com/egroupware
then in our external web server, we have in the listen.conf
a proxy pass
and a proxy pass reverse
from the /egroupware to https://egroupwareserver.mydomian.com/egroupware
also I recomend you to use https for external access and to require a valid client certificate, with SSLverifyclient require
of course, you must allow in your firewall to route to the internal web server. for this we use a different ip address for this traffic, and you need to have the proper settings in your firewall
hope this helps