You are planning an Azure Point-to-Site (P2S) VPN that will use OpenVPN.

Users will authenticate by an on-premises Active Directory domain.

Which additional service should you deploy to support the VPN authentication?

A. an Azure key vault

B. a RADIUS server

C. a certification authority

D. Azure Active Directory (Azure AD) Application Proxy

Reference:
https://docs.microsoft.com/en-us/azure/vpn-gateway/point-to-site-about