Log Message:
ap-rpaf-0.5, an Apache 1/2 module that twiddles the connecting client
IP and hostname information for backend servers that receive requests from
reverse proxies.

>From DESCR:
mod_rpaf 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 it's 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. It also takes the incoming X-Host header and
updates the virtualhost settings accordingly. For Apache2 mod_proxy it
takes the X-Forwared-Host header and updates the virtualhosts.