Instead of looking for an alternative for CGI::Application::Plugin::Authentication, how about devoting some effort to helping us work out whatever bugs there might be so that we can move closer to a stable release? While I can't speak for Cees, I'm pretty sure he'd appreciate more feedback and certainly more testers!
There is a CAP::Authorization package coming as well which is a natural extension to CAP::Authentication. You won't find a better authen/authz solution for CGI::Application.
Look for us in #cgiapp on irc.perl.org, or check out the wiki.
Hope to see you around,
MrCromeDome