libapache2-mod-rpaf binary package in Ubuntu Trusty amd64

 rpaf is short for reverse proxy add forward.
 .
 rpaf is for backend Apache servers what mod_proxy_add_forward is for
 frontend Apache servers. It does exactly the opposite of
 mod_proxy_add_forward written by Ask Bjorn Hansen.
 .
 It changes the remote address of the client visible to other Apache modules
 when two conditions are satisfied. First condition is that the remote client
 is actually a proxy that is defined in httpd.conf. Secondly if there is an
 incoming X-Forwarded-For header and the proxy is in its list of known
 proxies it takes the last IP from the incoming X-Forwarded-For header and
 changes the remote address of the client in the request structure.

Source package