If there is a repository that needs authentication with a long password or username (>64 chars) this is not handled well in apt. It will simply cut it off and the authentication will fail with a error from the server instead of indicating that the password is too long.
The maximum size of the user/password needs to be increased and a proper error message on overflow needs to be given.
To test this we need a repository with a long username/password.
= Test Case =
We'll use a pretend repository without any packages at murraytwins.com
1) Add the following line to /etc/apt/sources.list:
deb http://murraytwins.com/repository precise multiverse
2) Add the following line (yes, it's all one line) to /etc/apt/auth.conf (likely a new file)
machine murraytwins.com/repository/ login mrzx4l98d4tp89jab6giohdrjqysbyjs4npz2ccq25kvjmf5h8u4cmidcko7s4tfr6ur1teuv4ju1af-bp8wz2-hwbqs6tox1bv6csee9psn5309v7488f3dugifm692db2xfq8n1fsz7l87835tr0q36m2p3ftwpoqoy6 password password
3) Run apt-get update
4) Observe a 401 for murraytwins.com:
W: Failed to fetch http://murraytwins.com/repository/dists/precise/multiverse/binary-amd64/Packages 401 Authorization Required
With the version of the package from -proposed you'll receive a 404 instead of a 401.
To be clear it was fixed with this upload to quantal:
This bug was fixed in the package apt - 0.9.7.5ubuntu1
---------------
apt (0.9.7.5ubuntu1) quantal; urgency=low
[ Michael Vogt ]
* merged latest fixes from the debian-sid branch
[ TJ ]
* apt-pkg/
- increase LOGINSIZE/
if the limits are reached (LP: #1008289)