In a Windows domain, the domain controller is a server that handles authentication for the domain. The domain controller contains the Active Directory, which contains records for user accounts, service accounts, computers, and others.
The domain controller also contains the Kerberos key distribution centre (KDC). The KDC is a component of Kerberos, a secured authentication mechanism. For more information about Kerberos, see SASL Authentication.
Typically, only the domain administrators have access to the domain controller. When configuring FME Flow to integrate with Active Directory, there are certain steps that require access to the domain controller.