Setting up apache basic authentication behind a reverse proxy

I'm having difficulty passing htdigest authentication through a reverse proxy setup on machine A, to machine B, which requires the authentication.

I'm setting up a home development network, with all the basic tools (Trac, hudson, git, svn, etc..) Having gotten most of these set up and running, I'm looking to allow access to them from the outside. Each service is running on it's own VM, for management purposes. I've setup a reverse proxy that is the target for all the port 80 requests, and based on the path, redirects them to the correct server.

The problem behaves as follows. The trac page /login requires credentials, then redirects to the home page. The first time you access it, it asks for the credentials. But when it redirects you to the home page, you are not logged in, and any attempt to access the login page again, just immediately redirects to the home page.

My apache config is below:

ProxyPass /trac http://server1/trac
ProxyPassReverse /trac http://server1/trac

<Proxy http://server1/trac>
    Order deny,allow
    Allow from all
</Proxy>

#<ProxyMatch http://server1/trac/[^/]+/login>
#    LoadModule auth_digest_module /usr/lib/apache2/modules/mod_auth_digest.so
#    SetEnv proxy-chain-auth On
#    AuthType Digest
#    AuthName "trac"
#    AuthDigestDomain /trac
#    AuthUserFile /etc/apache2/trac.htdigest
#    Require valid-user
#</ProxyMatch>

EDIT: Some further reading indicates that trac relies on cookies for this type of user authentication, so I'm guessing I need to proxy cookies somehow.