When my commercial SSL certificate for OpenVPNAS from StartCom expired, I decided to switch back to using self-signed certificates for the same. This is fairly easy to do if you have root access to the appliance.
Just change directories to:
# cd /usr/local/openvpn_as/etc/web-ssl
and then execute this command for a 10 year certificate:
# openssl req -x509 -newkey rsa:2048 -keyout server.key -out server.crt -days 3650 -nodes
You will now need to restart the appliance (either by using sacli or just by restarting the appliance). Lastly, manually add the certificate to the browser to get rid of the security warning every time you logon.