You want to improve access control for your large OT network using passive authentication.

The correct answer is A. Fortinet Single-Sign On (FSSO) . The study guide states under Active and Passive Authentication that for passive authentication, “User does not receive a login prompt from FortiGate” , “Credentials are determined automatically” , and specifically “FSSO, RSSO, and NTLM can be used.” It then explains that passive authentication occurs with the single sign-on method and explicitly identifies Fortinet SSO (FSSO) as one of those methods.

The guide also says: “For passive authentication, you can implement FSSO. FSSO allows users who have already authenticated on the network through another system to be transparently identified. After initial login to any system on the network, users can access allowed resources without being prompted for credentials.” That is exactly what the question asks for: improving access control in a large OT network using passive authentication .

The other options do not match passive authentication. Local users are part of local authentication, two-factor authentication adds an extra security factor but still uses active authentication, and FortiAuthenticator as a remote server supports centralized authentication for mid-to-large networks, but by itself it is not the specific passive-authentication method being asked here. The study guide is explicit that the FortiGate configuration for passive authentication is FSSO .