On the security assist support page, there is a link for the current getting started guide:
securityassist/
the "How to apply Register/Login functionality to your checkout page" was written for Security Assist 1.x, though the concept is the same in Security Assist 2.
use the link on the support landing page for the security assist getting started guide instead of the link in the how to documentation.
I will forward your comments to the documentation team as well.