To enable remote users to access internal applications located behind an existing FortiGate SD-WAN hub, the customer must license the FortiSASE Secure Private Access (SPA) add-on.

Secure Private Access (SPA) Use Case: This specific add-on is designed to extend the Fortinet Security Fabric into the SASE cloud, allowing for a hub-and-spoke architecture where the FortiSASE PoPs act as spokes and the customer's on-premises FortiGate acts as the hub.

Licensing Requirements: The SPA add-on is a per-hub (per service connection) license. It provides the necessary entitlements to establish IPsec tunnels and BGP peering between the SASE infrastructure and the corporate FortiGate.

Feature Enablement: Once the SPA license is applied, the Configuration > Private Access menu becomes available in the FortiSASE portal. This allows administrators to define 'Service Connections' to their private data centers or cloud VPCs.

Analysis of Other Options:

Option A: The Global add-on is typically related to expanding the geographic reach or performance of the SASE PoPs, not specifically for private resource routing.

Option B: The Branch On-Ramp refers to connecting physical office locations (Thin Edge) to SASE, rather than the specific licensing for private application access for remote users.

Option D: Dedicated Public IP Address is used for source IP anchoring (SIA) to ensure remote users egress with a consistent IP for third-party SaaS IP-whitelisting.