In a hybrid authentication model with both certificate-based authentication for pre-logon and SAML-based multi-factor authentication (MFA) for user logon, the GlobalProtect agent processes the flow as follows:
During the pre-logon stage, the agent uses the machine certificate to authenticate and establish the initial VPN tunnel.
Once the user logs in (after the machine is connected), the agent then triggers SAML-based MFA to ensure the user is authenticated with multi-factor authentication, validating both the device and the user identity before granting full access.
This method ensures that both the device and user are properly authenticated and validated in the hybrid authentication model.

In the context of virtual systems (VSYS) on a Palo Alto Networks firewall, the external zone is typically associated with specific interfaces within a VSYS. Zones are fundamental security objects used to define traffic flow between interfaces, and the external zone would be used for interfaces that connect to external networks.
An external zone is associated with an interface within a VSYS of the firewall. This ensures that traffic from specific interfaces can be classified as belonging to the external zone, allowing the firewall to apply appropriate security policies.
The external zone is indeed a security object that is specific to a given VSYS, as each VSYS can have its own set of zones that are isolated from others.

Sandboxing executes suspicious files in an isolated environment and analyzes their behavior, making it effective against zero-day threats.

This approach best addresses the enterprise's requirements for certificate-based authentication, OCSP checks, and consistent policy enforcement:
Distributing the root and intermediate CA certificates via Panorama ensures that all firewalls in the enterprise are consistent in their trust chain and can validate certificates properly. Configuring OCSP responder profiles on each firewall offloads the revocation checks to an internal OCSP server, which reduces the overhead on the firewalls and ensures fast, real-time certificate status checks.
Using CRL checks as a fallback ensures reliability in case the OCSP responder is unavailable.
Separate certificate profiles for users and devices ensure that the firewall can enforce different security policies based on the type of certificate (user vs. device). Automated certificate enrollment methods such as Group Policy or SCEP streamline certificate distribution to endpoints, ensuring efficient management of certificates across geographically dispersed firewalls.