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A mod_rpaf story.

My Apache virtual hosts are dynamically configured from a library of Perl code using PerlSections.
A configuration file for one virtual looks something like:

<VirtualHost *:80>
  require 'conf/lib/';

Aside from boostrapping all the basic virtual host configuration, establishes basic authentication (via mod_auth_tkt) for the <Location /> of the virtual host. Authentication is the desired default but, for some specific virtual hosts, I want to disable the authentication requirements. This I can do by appending a new <Location /> after the Perl Section.

<VirtualHost *:80>
  require 'conf/lib/';
 <Location />
  Allow from any

This effectively overrides the deny from declared by the perl library and makes the site public. This has been working fine for me for years. Recently though, I put an Nginx reverse-proxy in front of some of my virtual hosts and installed mod_rpaf into Apache so the IP address it logged would be the client’s and not the proxy server.

There I hit a snag. Apache/mod_rpaf was ignoring the X-Forwarded-For header and only logging the IP address of the proxy. Actually the GET '/' request was logging correctly, but that was insufficient and no consolation.

Client logging was done correctly if I used a static, hand-crafted Apache configuration file (not using the Perl library) so I knew mod_rpaf was installed correctly. I began to suspect the dynamic Perl configuration and that made me nervous; I really didn’t want to give that up completely.

Well, cutting to the chase, it turns out that the ‘Allow from any’ added to disable the basic authentication was the culprit. I’ve been using ‘Allow from any’ for years and it does indeed allow any host access but looking at it anew today it suddenly struck me as being wrong. It’s normally ‘Allow from all‘, I must have had ‘Satisfy any‘ on the brain when I originally started using the override – propagating around through thoughtless copying/pasting. On a whim I changed it to ‘Allow from all‘ and, w00t!, mod_rpaf began logging the correct client address.

Are ‘allow from any’ and ‘allow from all’ supposed to mean different things to Apache? A little Googling turns up examples of people using ‘allow from any’ but I don’t see any indication that it has a special meaning.

I’m using the Apache mod_rpaf module to capture client IP addresses in the X-Forwarded-For header passed by an Nginx reverse proxy. This is good for logging and CGI environments but mod_rpaf does not fix up the client IP address sufficiently to be used in Apache’s allow/deny access control directives.

Almlys has a nice workaround.

Quoting the juicy bit from Almlys’s blog posting:

SetEnvIf X-Forwarded-For ^172\.26\.0\.17 let_me_in
Order allow,deny
allow from env=let_me_in



October 2008