Asset paths should be constructed using the BaseURLSource rather than just the request context path to match the behavior for pages, etc. Currently, to get absolute URL's including domain portion for assets, you need to override the AssetPathConstructor.
Apart from contributing the BaseURLSource, it is a small change from:
StringBuilder builder = new StringBuilder(request.getContextPath());
StringBuilder builder = new StringBuilder(baseURLSource.getBaseURL(request.isSecure()));