I have been looking through java web frameworks lately (though this question need not be limited to java), and I noticed that most examples on web framework websites leave out auth & auth examples in their stock documentation.
one ruby example: acts_as_authenticated (link?)
grails has: http://www.grails.org/Authentication+Plugin
Anyway, please throw up some links to your framework of choice, and a link to a nice walkthrough to implementing an auth&auth solution.