<VirtualHost *:80>
# Enable forward proxy
ProxyRequests On
# Add "Via" header
ProxyVia On

<Proxy *>
  Order allow,deny
  allow from all
</Proxy>

ErrorLog "/var/log/apache2/proxy-error.log"
CustomLog "/var/log/apache2/proxy-access.log" common
</VirtualHost>

/etc/apache2/sites-enabled/000-default.conf