This Plugin gives WordPress, Buddypress and bettercodes - with oAuth a Single-Sign-On - login and singup functionality.
Yes you need your own API-Key for every single social-network.
Please go to: http://msdn.microsoft.com/en-us/library/ff751474.aspx
Go to https://developer.apps.yahoo.com/projects and add new Project. Please notice that you need to enable the permission "Read/Write Public and Private" in the Profiles section. The e-mail adress to singup is part of this section.