OAuth
http://oauth.net
http://oauth.net/2/
http://tools.ietf.org/html/rfc6749
人人网:http://wiki.dev.renren.com/wiki/Authentication
新浪微博:http://open.weibo.com/wiki/index.php/Oauth
http://blog.csdn.net/seccloud/article/details/8192707
http://www.ruanyifeng.com/blog/2014/05/oauth_2_0.html