[AuthenNTLM, mod_proxy] Apache2::AuthenNTLM fails to work with mod_proxy

[Konstantin Khomoutov <fl...@users.sourceforge.net>]

I want to implement NTLM-based access to CUPS. CUPS doesn't support
that by itself so I've decided to make it listen strictly on
127.0.0.1 and "export" it via a local Apache's vhost using mod_proxy.

Here's my vhost setup:

---8<--[cut start]------------------------------------------------

<VirtualHost *:80>
    ServerName  cups.jukebox.domain007.com
    ServerAlias printer.jukebox.domain007.com

    ServerAdmin webmaster@proxysrv.domain007.com

    ProxyRequests off
    ProxyPass       /   http://localhost:631/
    ProxyPassReverse    /   http://localhost:631/

    <Location />
        PerlAuthenHandler +Apache2::AuthenNTLM
        AuthType ntlm,basic
        AuthName "Admins Only"
        PerlAddVar ntdomain "DOMAIN007 rras bercut"
        PerlSetVar defaultdomain DOMAIN007
        PerlSetVar splitdomainprefix 0
        PerlSetVar ntlmdebug 1
        PerlSetVar ntlmsemtimout 10
        Require valid-user

        Order deny,allow
        Deny from all
        Allow from 127.0.0.0/255.0.0.0 192.168.0.0/255.255.0.0
    </Location>

---8<--[cut end]--------------------------------------------------

This works OK in two cases:
1) All AuthenNTLM stuff is commented out (and then there's no
authentication of course, but I can manage CUPS);
2) mod_proxy's stuff is commented out (and then there IS
authentication, but Apache just shows some directory index since
no proxying is performed).

Various tweakery of mod_proxy like disabling cacheing, turning ProxyVia
off and the like yielded no results.

Please help!

System info:

OS: Debian Sarge 3.1
Apache: 2.0.54 (prefork model)
mod_perl: 2.0.1
Apache2::AuthenNTLM: 0.02