The Two-Factor Authentication Parameter
Two-factor authentication (2FA) allows you to require users to additionally enter a time-based one-time password (TOTP) generated using their mobile applications (e.g. Google Authenticator) to log in to a Client computer.
If the Enable two-factor authentication checkbox is selected (on the Editing Client / Editing Client Group page, on the Authentication Options tab, scroll down to the Two-Factor and Secondary Authentication section) to enable this option, the Client will display an additional window to prompt the user to enter the TOTP during login to Linux.
NOTE: Two-factor authentication can only be enabled while editing a Client (or Client group) in the Management Tool.