It seems that Ingress is implemented in a particular way that prevent any third party web interface to works correctly with relative url contained in web pages.
In order to obtain a better integration, is possible to manage ingress like a standard reverse proxy, using the custom INGRESS subpath as the incoming request path in addon server?
This could bring the add-on integration easier… At the moment, no way to integrate a third party web component without rewriting all resource paths.