I currently run a couple of projects where we need to implement a Security Service for Authenticating and Authorization users.

Two videos by Dominick of ThinkTecture fame:

What and Why is Claims and Tokens

Dominick Baier - Authentication & Authorization in .NET 4.5 - Claims & Tokens become the standard Model from NDC Conferences on Vimeo.

Securing ASP.NET Web APIs and HTTP Services

Dominick Baier: Securing ASP.NET Web APIs and HTTP Services from NDC Conferences on Vimeo.