We Currently have Sage 100 running on a Windows Server 2012 R2, which is also the network's Domain Controller. Everyone uses Windows Authentication to login.

We are soon going to add a bigger and faster server running Windows Server 2019. Everything will move to the new server (Domain controller, Active Directory, etc.) except for Sage, which is staying on the old server. 

My question is, since the server that Sage will be on will soon stop hosting Active Directory services, what do I need to do to point it to Active Directory in the NEW server so users can still login to Sage using Windows Authentication?