Following the security principle of trust no one, I can't use a service like http://www.serfish.com/. Is there a free software program that I can install on my Ubuntu server to give me secure shell access via a web-interface?

I would prefer a small and light-weight solution, so that I can do at least a rudimentary audit of the source code. I would also prefer something that is in the 'main' repository, so that I get the benefit of stable release upgrades.