大部分企业使用 java 开发业务系统， 针对java cas的认证 demo 比较多 ，还有PHPCAS ，标准的参考这里：
整理登录流程如下图，图片来自网络
找了不少资料，nodejs 实现的比较少，npm 上库很多，试用了好几个才成功。
推荐这里库 connect-cas
注意参数解析
Many of these options are borrowed from node's url documentation. You may set global options through the .configure() method or override them with any of the exposed middleware.
- procotol ：The protocol to communicate with the CAS Server. Defaults to 'https'.
- host ： CAS server hostname
- port ：CAS server port number. Defaults to 443.
- gateway ： Send all validation requests through the CAS gateway feature. Defaults to false.
- paths
- serviceValidate Path to validate TGT
- proxyValidate Path to validate PGT (not implemented)
- proxy Path to obtain a proxy ticket
- login Path to the CAS login