This document summarizes a presentation about building an OAuth-as-a-service API using ASP.NET Web API and Windows Azure. The presentation introduces APIs and their benefits, describes API characteristics like HTTP verbs and status codes, demonstrates how to build an API with ASP.NET Web API, discusses securing APIs with OAuth2 and using Windows Azure Access Control for OAuth delegation to manage authentication. The key takeaways are that APIs are becoming the new way applications connect to services, they are valuable, should use HTTP, and ASP.NET Web API and Azure ACS can help build and secure OAuth-based APIs.