FW: web based registration/login question

Hi... I have a generic question. I'm posting it here in the hopes that someone might have a strong opinion as to where I might turn... I'm in need of a general app that can be used to perform strong authentication for registering/loggin in users. As I'm going to be dealing with a couple of sites, I'd like to create the underlying structure/functionality once, and resue it as I need to. The OS will be Windows/Linux.... I've seen a number of apps from google.. but I'm not sure how good/complete they are. I could use a Perl/PHP based app.... I need strong password protection IP based Possible individual page protection from non-logged/registered in users Admin functionality for setting up/authorizing users... Etc... I'd like to be able to create a test website, and get all the functionality working/tested... and then roll out the other sites..... However, I don't really want to spend an inordinate amount of time going down the wrong path if there's already a good solution that I could adapt to my needs..... Oh, I'm also looking for an Open Source solution.... Thanks for your time on this.... Thanks Bruce Douglas bedouglas@earthlink.net (925) 866-2790