IndieAuth – A federated login protocol using one's own domain name
From what I understand this handles only authentication and provides tokens that may be used for additional (undefined APIs).What bugs me about this (and all the oAuth implementations out there) is that you never just want authentication. You also want to know things about the user (username, name, email, avatar, etc) - but to get this you have to implement a plethora of APIs for the various services, because they are all different. I wish fetching profile info would be part of the standard.