You have the following on-premises servers that run Windows Server: - Two domain controllers in an Active Directory Domain Services (AD DS) domain - Two application servers named Server1 and Server2…

Azure AD Application Proxy publishes on-premises web applications through the Microsoft cloud, requiring Azure AD authentication before any traffic reaches the internal servers. This eliminates the need for inbound firewall ports or a VPN endpoint exposed to the internet, directly reducing the attack surface. It aligns with Zero Trust principles by verifying identity explicitly and granting per-application access rather than broad network access.

Configuring the VPN to use Azure AD authentication improves authentication security but still exposes the VPN endpoint to the internet and provides broad network-level access, contradicting the Zero Trust principle of minimizing the attack surface.

Microsoft Defender for Cloud Apps connectors and rules govern access to cloud SaaS applications and do not provide a secure access path to on-premises ASP.NET web applications.

Web protection in Microsoft Defender for Endpoint is an endpoint security feature that protects devices from malicious web content; it does not control or secure remote user access to internal web applications.