Open Single Sign-On
https://github.com/keycloak/keycloak
http://jasig.github.io/cas/4.1.x/index.html
http://www.zhihu.com/question/25400195
http://www.josso.org/confluence/display/JOSSO1/JOSSO+-+Java+Open+Single+Sign-On+Project+Home
https://www.forgerock.com/products/access-management/
http://www.manageability.org/blog/stuff/single-sign-on-in-java/view
http://doc.sdk.tango.me/index.html
http://www.codeproject.com/Articles/746569/Sharing-Experience-of-SSO-Integration-via-SAML-Res
http://merbist.com/2012/04/04/building-and-implementing-a-single-sign-on-solution/