Chapter 4: Configuration > 4.2 Configuration Variables > 4.2.2 Server Configuration Variables >

WINNT-LOGON-DOMAIN

This variable applies only to Windows servers. Set it to the name of the Windows domain to log users onto. For this variable to have an effect, you must set the SECURITY_METHOD variable to "LOGON". Note that if the domain does not exist, users are denied access to the server.