Please read for an updated status on RailsCasts:
Learn more or hide this
GitHub User: c4ftabrez
@lazylester - you probably got an answer already.
The screencast and what Ryan mentioned are indeed authentication because they help you keep trail of all activities for a digital identity. This is what most public websites need. But if you need some link between the physical person and digital id (for example to prevent 1 person from having multiple accounts) you can use an approval flow. Look at authentication gems such as devise. Devise allows you to mandate approval of new registration.
There are other strategies worth looking at too. For example, Google encourages people to link their account(s) to a mobile number. That way even if a person has multiple google accounts, they can be linked together via a common mobile number. You need to decide what works for your application.
I hope that helps.