The presentation gives a good introduction to authentication and the options available today, particularly for Ruby. With systems like OpenID or CAS, it's possible to delegate the task of authenticating a user (ie. letting the user log in). Instead of writing code for authentication, OpenID and CAS servers handle everything involved. The presentation also shows how to install these servers, which is useful for companies that want to keep the authentication server internal.
For a overview of how to get started with these technologies, Justin shows how to develop for both OpenID and CAS and builds three applications using these systems.
Watch "Security (CAS and OpenID) with Ruby".