I needed the forwarded host on a backend mod_perl server from mod_proxy under Apache 1.3. The mod_perl docs show how to accomplish this for IP by parsing the X-Forwarded-For header in startup.pl and setting $r->connection->remote_ip to that value. To avoid patching mod_proxy I added a few lines to mod_perl's My::ProxyRemoteAddr that sets $r->header_in('Host') to the value of the X-Forwarded-Host header.

It works but a question remains since I can't find examples online of sane people doing it this way. Is this a sound approach? If not, please correct me. If so, maybe the already very excellent mod_perl docs could benefit by adding this information. Thanks for your consideration. 

sub My::ProxyRemoteAddr ($) {
  my $r = shift;

  return Apache::Constants::OK
      unless ($r->connection->remote_ip eq "127.0.0.1")
          and $r->header_in('X-Forwarded-For')
          and $r->header_in('X-Forwarded-Host');

  if (my ($ip) = $r->header_in('X-Forwarded-For')  =~ /([^,\s]+)$/) {
    $r->connection->remote_ip($ip);
  }
  if (my ($fh) = $r->header_in('X-Forwarded-Host') =~ /([^,\s]+)$/) {
    $r->header_in('Host',$fh);
  }
  return Apache::Constants::OK;
}

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In reply to mod_perl ProxyPreserveHost Emulation by Anonymous Monk

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