This is a definitive guide to the OAuth 2 protocol. It covers the latest version of the OAuth 2 core specification (currently the spec is at draft 21 but very little will change between now and the final version). The book will help beginners get started writing client applications to interface with a number of APIs currently using OAuth 2, and will help experts develop and improve their server-side solutions. It is for both developers and engineering managers who want to develop web services with secure APIs, and covers high level overviews as well as details on the security implications of the protocol.