The link refers to PHP_AUTH_USER which makes sense for PHP. A more generic term is more common in other frameworks I think. AUTH_USER is what I would expect to use in RubyOnRails, and I think IIS already provides this variable when using NTLM authentication. Making sure that this AUTH_USER is available...

Ruby on Rails (http://www.rubyonrails.com/) support would be excellent! I actually need this in production yesterday, so it would be great to get vendor supported FCGI rather than the hacking I'm doing now to make it work (actually it still doesn't work and I may have to switch to Apache.)