NPS: Default User Identity
Applies To: Windows Server 2008, Windows Server 2008 R2
You can use the Default User Identity registry setting to provide Network Policy Server (NPS) with a standard user account with which to perform authentication and authorization when the user name is not present in the connection request.
User identity is the means by which NPS identifies the user for the purposes of authentication and authorization. Normally, the user identity is the string value of the User-Name Remote Authentication Dial-In User Service (RADIUS) attribute. If the User-Name attribute is not present, or is present but equals null, the user identity is set to the Guest account or the account specified by the Default User Identity registry value.