Thanks for the compliments, @codetricity!
Yes, that is basically how it works. To help explain, here's the first login modal:
When you click either the Click here to sign in button or the Create New Relic Account link within the login modal, we return you back to the site with information gathered from our authentication system. In this case, we only return your email address.
We then display a 2nd login modal:
As you can see, this modal includes your Email (not editable), a best guess attempt at your Name, and a suggestion for your Username. The latter two are based on your email address. If you're not satisfied with our suggestions for your Name and Username, you can change them at this point. That is the sole purpose of this 2nd login modal.
You could skip this 2nd login modal by (1) returning the user's name from your authentication system and (2) auto-assigning usernames (note: you can always go to your user preferences page and edit your username). We chose not to do it this way because (1) our authentication system does not store users' names (we store this info in a separate service) and (2) we wanted to allow users the ability to select their username as part of the login process.
@sam wrote up a topic on Discourse's forum that discusses how to amend current user logic to integrate your own authentication system. This is exactly what we did. My opinion is that the method is fairly straightforward, but getting it to work for your authentication system can be challenging since each authentication system is a bit different. What I mean by that is that if you have questions, you may not be able to reach out to the community for help since you may not want to share the internal workings of your authentication system. That being said, if you do run into any issues, I'm happy to try and help out. Good luck!