As you know, in previous NAV versions (3-tier) you can access the system by using 4 different authentication types:
- Windows
- UserName
- NavUserPassword
- AccessControlService
A thing that I think is passed under the hood in these days is that now NAV 2016 supports also the SQL Authentication.
Configuration for this authentication type is a bit tricky but you can find all the details here.
Stefano Demiliani 