Thank you!
I am planning to do yet another article on authorization in some time and I’ll consider using AJAX 
Regarding the “errors” partial - yeah, I absolutely forgot to mention it. The actual code for it is on GitHub https://github.com/bodrovis/SitePoint-Sorcery/blob/master/app/views/shared/_errors.html.erb This is a pretty simple partial for rendering errors found while submitting the form. I prefer to do it this way because you may have many different forms and only one partial for errors. I can explain this in a more detail if it is needed.