You use vCenter Single Sign-On to authenticate and manage vCenter Server users.

In vCenter Server versions earlier than vCenter Server 5.1, when a user connects to vCenter Server, vCenter Server authenticates the user by validating the user against an Active Directory domain or the list of local operating system users. In vCenter Server 5.1, users authenticate through vCenter Single Sign-On.

The Single Sign-On administrative interface is part of the vSphere Web Client. To configure Single Sign-On and manage Single Sign-On users and groups, you log in to the vSphere Web Client as a user with Single Sign-On administrator privileges. This might not be the same user as the vCenter Server administrator. Enter the credentials on the vSphere Web Client login page and upon authentication, you can access the Single Sign-On administration tool to create users and assign administrative permissions to other users.

vSphere 5.1 users have the option of logging in to vCenter Server with the vSphere Client or with the vSphere Web Client.

Using the vSphere Client, you log in to each vCenter Server system separately. All linked vCenter Server instances are visible on the left pane of the vSphere Client. The vSphere Client does not show vCenter Server systems that are not linked to the vCenter Server that the user logged in to unless the user connects to those vCenter Server systems explicitly. This behavior is unchanged from vCenter Server versions earlier than version 5.1.

Using the vSphere Web Client, you authenticate to vCenter Single Sign-On by entering your credentials on the vSphere Web Client login page. You can then view all of the vCenter Server instances for which you have permissions. After you connect to vCenter Server, no further authentication is required. The actions that you can perform on objects depend on the user's vCenter Server permissions on those objects.

For versions earlier than vCenter Server 5.1, you must explicitly register each vCenter Server system with the vSphere Web Client. For vCenter Server 5.1, vCenter Server systems are automatically detected and are displayed in the vSphere Web Client inventory.