I don't seem to have one handy. ;) Have you watched the screencast I linked to yet? This isn't a ready-made solution; it's a set of tools that you as a programmer can use to build your specific application.

The screencast is good. So is the Mojo::UserAgent documentation. Its SYNOPSIS section shows a brief demonstration of non-blocking UserAgent requests, which it what you will need if you're going to load test a login system.