Configuring Apache HTTP for changing context URL

First of all you must have one of these configurations running on your server:

Configuring Apache HTTPS Reverse-Proxy

 Enable the headers module:

$ sudo a2enmod headers

 To change /OpenKM application context try this as your VirtualHost configuration:

<VirtualHost *:80>

  ProxyPass / ajp://localhost:8009/OpenKM/
  ProxyPassReverse /

RequestHeader edit X-GWT-Module-Base ^(*)$ $1/OpenKM/frontend/$2
  ProxyPassReverseCookiePath /OpenKM /

  ErrorLog /var/log/apache2/openkm-error.log
CustomLog /var/log/apache2/openkm-access.log combined

You need also set the configuration parameter system.apache.request.header.fix to on (true). 

Additional information