User login with omniauth on Rails and set anonymous username or alias

I am very new to Rails and before I get deep into the building process, would like to know if anyone knows of a way (or any articles--I've been searching and can't find exactly what I'm looking for) to do the following:

1) have a user login using omniauth 2) after logging in directing the user to set an anonymous username that will what shows for this user throughout the activity in the application (all omniauth use info remains private)

Is there a way to do this? I found this question login using facebook or create an account but I'm essentially having them login using facebook AND set an account of a sorts.

If anyone has any resources that could point me in the right direction, I'd appreciate it!