The correct answer is D. zero trust network access (ZTNA).
Explanation:
Zero Trust Network Access (ZTNA) is the FortiSASE feature specifically designed to provide secure, least-privileged access to applications. It operates on the core principle of "never trust, always verify." Instead of granting broad network access like a traditional VPN, ZTNA grants access to specific applications on a per-session basis, only after verifying the user's identity and the security posture of their device. This ensures a user can only access the corporate applications they are explicitly authorized for, and nothing else on the network, perfectly embodying the principle of least-privileged access.
The FortiSASE solution achieves this by creating a secure, encrypted tunnel from the remote user directly to the application protected by the on-premises FortiGate, which acts as a ZTNA access proxy.