User authentication for non-domain workstation

Hi all,

we'd like to do as follows:

a consultant use is own laptop, put the lan cable on, receives an ip address and soon receives a pop-up, or a web browser window, prompting for domain credentials, after authenticated all services are granted.

We've got alreay fortiguard firewalls and fortiauthenticator with some forticlient (ems too) installed.

Thanks in advance.