I assume you are using Caché on Windows, and you are launching Terminal from the Cube on the local desktop of the PC where Caché is running.
In this case the security settings of the %Service_Console service (System > Security Management > Services) are what you need to adjust.
Enabling only "Unauthenticated" will mean that you don't get prompted for username/password, and your Terminal session will report $username="UnknownUser". But the security settings for UnknownUser will also have to allow that account to get to the programmer prompt. If they don't, your Terminal session won't start.
Enabling only "Operating System" will mean that provided a Caché user account exists that matches the Windows account you are logged into the desktop as, your Terminal session will report that username as its $username. Again, the Caché account will need sufficient permissions to get to the programmer prompt.