In the FortiSASE architecture, there are two primary methods for delivering Secure Internet Access (SIA): Agent-based (using FortiClient) and Agentless (using Secure Web Gateway/SWG).

Use Case Analysis: The scenario describes a contractor—an unmanaged user—who requires temporary access for a web-based application (the POS system). For contractors or guests using personal/non-corporate devices where installing the FortiClient agent is either not feasible or not desired, FortiSASE provides the SIA Agentless deployment model.

Mechanism (SWG & PAC): In this mode, FortiSASE functions as an explicit web proxy. To steer the contractor's web traffic (HTTP/HTTPS) to the SASE cloud for inspection, the administrator provides the user with a proxy auto-configuration (PAC) file. The contractor simply configures their browser or operating system to point to the URL of this PAC file.

Security Enforcement: Once the PAC file is applied, all web traffic from the contractor's device is redirected to the FortiSASE SWG PoP. Here, the traffic is subject to the organization’s full security stack, including SSL deep inspection, Antivirus, Web Filtering, and Application Control, ensuring that even temporary contractor access is fully secured and logged.

Why other options are incorrect:

Option B (Tunnel Policy): This refers to agent-based access where a VPN tunnel is established. This requires FortiClient, which is generally not used for temporary contractors on unmanaged devices.

Option C (ZTNA Unmanaged): While ZTNA supports agentless access to private applications (SPA), providing internet access (SIA) to an unmanaged endpoint is specifically the role of the SWG/Proxy service.

Option D (Self-registration): While FortiSASE has a User Portal for onboarding, it is a method for user registration/credential management, not the technical traffic-steering mechanism used to provide internet connectivity.

According to the FortiSASE 25 Secure Internet Access Architecture Guide, the SWG (Agentless) approach is the recommended best practice for securing web-only traffic from unmanaged endpoints and third-party contractors.