Fortiauthenticator with Windows Terminal server for 2FA

I wanna share a scenario with you, I have a Customer they are simply using Windows Terminal server to access their Internet Servers. They want to deploy FortiAuthenticator with Terminal Server so that any allowed user should access this Terminal server using 2FA from Fortiauthenticator. Is it possible to deploy only a Fortiauthenticator will cover their requirement? there is no fortigate in the environment i can't find any Manual about this, Kindly help me step by step how to deploy it. We already did configure the FortiAuthenticator VM, Just waiting for the confirmation from you. So that we will go for Licensing of the Fortiauthenticator Unit. Thanks and Regards Khan