OAuth2 in action is a fantastic walk-through of the OAuth2 delegation protocol, aiming at developers and implementers. The way Justin guides the reader through the "do and don't" of OAuth2 is always balanced and full of practical advices. You won't certainly venture in building your own OAuth2 client or server, but knowing the ins and outs of OAuth2 is absolutely a must to work proficiently with any vendor's SDK when the time comes.