The web server that is in ConfD Premium is based on the Yaws web server. It is embedded inside the ConfD daemon and cannot be replaced. You could proxy another server in front of the ConfD web server.
Another possibility is to do the work to integrate a web server to the Management Agent API (MAAPI) and not use the ConfD web server. However, there would be a lot of time savings from using ConfD Premium and it's pre-integrated web server.