[Google-Desktop] Authenticated RSS Feeds

I am trying to get an authenticated RSS feed added to the Google
Desktop Web Clips Plug-in, and I keep getting the following error:

Web Clip Error: Unknown error

The RSS feed works successfully if I do not require an authenticated
user, so it's not a problem with the feed itself (that I can see). Due
to security requirements at my office, they require content on the site
I pull this from to use authentication, so just leaving it anonymous is
not an option.

I've tried multiple combinations to embed the username and password the
URL, including no username and password, just a username, both username
and password, etc.

If it helps, the feed is being generated by Trac
<http://projects.edgewall.com/trac/> 0.9.2, and I am trying to pull in
the Timeline feed. Logins work successfully under normal web browsers
that support standard HTTP Authentication (Firefox, IE, etc.) I am
using Apache 2.0.53 on Fedora Core 3, using Kerberos authentication
against an Active Directory server (usernames appear as
username@DOMAIN.COM in the AUTH_USER variable).

I'm also going to run this by the Trac IRC channel to see if they have
any ideas.