Apache2 – Reverse Proxy with Authentication on Windows 7

I am trying to setup an Apache2 reverse proxy from my laptop (Windows 7, Apache 2.2.17) to a Nexus server (Windows Server 2003) on our network. This is just a test before setting this up for real on an Internet-visible server that we have. I can get the proxy itself setup and proxying Nexus beautifully. But when I try to apply authentication to the proxy, that's when things go wrong. I want to listen on port 8090.

Here are the relevant bits from my httpd.conf file:

Listen 8090

ProxyRequests Off
ProxyPreserveHost On

<Proxy /nexus>
    Order deny,allow
    Allow from all
</Proxy>

<Location /nexus>
    Order deny,allow
    Allow from all

    ProxyPass http://secret.mydomain.com:8082/nexus
    ProxyPassReverse http://secret.mydomain.com:8082/nexus

    AuthType Basic
    AuthName "Nexus"
    AuthBasicProvider file
    AuthUserFile c:\tmp\users

    Require valid-user
</Location>

If I comment out all the Auth* directives, the proxying to Nexus works a treat using a URL like http://localhost:8090/nexus/content/groups/central/ But once I add those Auth* directives back in, I get a login box, enter valid credentials, and then it prompts again. And again. And again. The one thing I noticed, is that the first time the credentials dialog appears, the realm shows up as "Nexus" (as I have it in httpd.conf). But on all subsequent prompts, it shows as "Sonatype Nexus Repository Manager," which, I assume, is coming from the Nexus server itself, even though it doesn't require authentication.

Also, I know that the password file and user/password are good, because if I setup authentication using them just for a local directory, it works fine.

I've found various blog posts about reverse proxies, and about authentication, but I just can't seem to make them work together. I've tried many things, but this is the problem distilled down to its simplest, I think.

Does anyone see anything blatantly wrong with my config? Or anything subtly wrong with it?