Computers on a Workgroup do not use an external PC (Domain Controller with the Active Directory) to help with the process of Authentication. Instead, they rely on their own information for Authentication.
Suppose an OPC Client application, which resides on a Workgroup, communicates with an OPC Server on a Domain. In this case, the OPC Client application’s User Account must either exist on the Domain Controller (of the OPC Server PC), or on the OPC Server PC itself. Furthermore, the User Account of the OPC Server must exist on the OPC Client application’s PC.
Suppose that an OPC Client application that resides on a Domain communicates with an OPC Server on a Workgroup. In this case, the OPC Client application’s User Account must exist on the OPC Server PC itself. Furthermore, the User Account of the OPC Server must either exist on the Domain Controller (of the OPC Client PC), or the OPC Client application’s PC.