参考资料:
原理流程
http://www.ibm.com/developerworks/cn/websphere/library/techarticles/1111_luol_sso/1111_luol_sso.html
http://blog.csdn.net/csethcrm/article/details/20694993
opensaml插件
https://wiki.shibboleth.net/confluence/display/OpenSAML/Home/
代码实现