Undertow 4 in Wildfly 10 can add some kind of authentication to limit the access to static resources:
Example:
http://localhost/img/my_img.jpg -> will return will return 401 Forbidden
http://localhost/img/my_img.jpg&auth=some_app_key -> will return 200 OK
http://localhost/img/my_img.jpg -> with a valid header parameter will return 200 OK
For serving static content this is a good example : How to configure Wildfly to serve static content (like images)?
