下载CA root 证书
http://adip/certsrv
server error or refuse to connect
这是由于AD上没有安装Active Directory Certificate Services 或是Active Directory Certificate Services下安装的服务不正确
解决方法：
打开server manager， Add Roles and Features Wizard, 勾选Active Directory Certificate Services以及Active Directory Certificate Services下面的Certification Athority和Certication Athority Web Enrollment
配置Active Directory Certificate Services
配置完成后再次打开 http://adip/certsrv，可以下载ca certificate
