Enable Windows Active Directory Authentication in vSphere 5.1.

vSphere Single Sign On is a new feature in vSphere 5.1, vSphere SSO controls authentication service, so you  can no longer  add new authentication provider in vCenter by standard vSphere client. It has to be done in vSphere webclient, which can talk to vSphere SSO service.

Steps to add Windows Active Directory provider.
1.Create a generic user in AD for LDAP search, define user and group base DN.
2.Install Webclient from vCenter installation media, just like vSphere Client, it doen’t need to be installed on vCenter server.
3.Launch Webclient https://client-ip:9443/vsphere-client and login
The account used for login is important, if you installed SSO service when login with local account, local account can  login Webclient, But it doesn’t  have permission to configure SSO, you have to login with the default SSO account “admin@System-Domain” created during installation.
4.Navigate to Administration/Sign-on and Discovery/configuraiton( the configurion node won’t be shown, if login with local Windows account), and add “+” sign to add identity sources.
The login credentials will be sent in clear text with ldap, if it is a concern, enable ldaps by creating certificate
The username should be in LDAP syntax, find the exact string in ADSI edit tool in AD.