The RestAuth project provides APT repositories for all software it maintains. Packages are available for almost all distributions that are currently maintained. For Ubuntu, this includes 9.10 (karmic), 10.04 (lucid) and 10.10 (maverick). For Debian, packages are currently only available for squeeze a.k.a. the current testing.
To add the repositories, simply add this line to your sources.list file:
deb http://apt.fsinf.at <dist> restauth
... where <dist> is any of the supported distributions (karmic, lucid, maverick or squeeze). After that, you have to:
apt-get update apt-get install fsinf-keyring apt-get update
... to be able to install any of the RestAuth packages.