Disguise Backend DNS

I am trying to disguise the DNS of the backend’s webserver.
If the config would be simple as:

frontend https-frontend

    bind xxx.xxx.xxx.xxx:443 ssl certificate.pem

    # General Rules
    acl path_is_root path -i /

    # Rules 
    acl host_oldserver hdr(host) -i oldserver.domain.com

    use_backend newserver-backend if host_oldserver

backend newserver-backend
server newserver newserver.domain.com:443 check ssl verify none

The goal is that if you enter “https://oldserver.domain.com” it doesn’t show “https://newserver.domain.com” in the browsers address bar - it should always show “https://oldserver.domain.com/.*”.
I already messed around with “http-response set-header …” in the backend, but I seem to miss something?