[1] Final: OpenID Authentication 2.0 - Final ( 版) http://openid.net/specs/openid-authentication-2_0.html
[2] Final: OpenID Provider Authentication Policy Extension 1.0 ( 版) http://openid.net/specs/openid-provider-authentication-policy-extension-1_0.html
Important: Google has deprecated OpenID 2.0 and will shut it down after a migration period. If your app uses OpenID 2.0, you must migrate your app by the shutdown date April 20, 2015, as shown in the migration timetable.
All of the keys in the request message MUST be prefixed with "openid.". This prefix prevents interference with other parameters that are passed along with the OpenID Authentication message.
[5] Yahoo! OpenID - YDN ( 版) http://web.archive.org/web/20120114224508/http://developer.yahoo.com/openid/
livedoor Auth が提供するOpenID機能では http://profile.livedoor.com/<あなたのlivedoor ID> という形式のURLが作成でき、そのURLをIDとしてOpenID認証が利用出来るようになります。
また、OpenID2.0に対応しておりますので http://livedoor.com/ だけでも認証が可能です。