Apache is a reverse-proxy to my app. A client requests
GET /foo/images/logo.png HTTP/1.1 Host: cdn.example.com
I want Apache to modify the request so that the app on the other side of the reverse proxy receives it in the format
GET /images/logo.png HTTP/1.1 Host: foo.example.com
Rewriting the URL is easy, but I haven't found a way to modify the Host header with a value extracted from the URL. Is this possible?