Apache gethauthuser() - Cold Fusion

We are using Coldfusion 8 on Debian Linux and Apache 2.

I am able to get the server to request Active Directory credentials from a
user similar to the IIS "Require authentication" function using authnz_ldap
module. This will force the user to authenticate using there active directory
user name and password before they are allowed on part of the site.

The problem is that Coldfusion does not seem to capture the login information
using #getauthUser()#. However this function does work on a Windows based
server when IIS is configured to "Require user Authentication", and the client
logs into the site.

I've tried a few variants of cgi.auth_user and the like but all return with
"[empty_string]". Can anyone provide some insight on how to extract this kind
of information for our Linux based server.