When the ProxySG uses a virtual URL for user authentication, what must the virtual URL point to?

The correct choice ensures that the virtual URL points to a hostname capable of DNS-resolving to an IP address. This is essential because the ProxySG needs to establish a connection to the specified address for user authentication to function correctly. When users attempt to authenticate, the system relies on being able to resolve the hostname to a valid IP, enabling it to communicate effectively with authentication services, whether they are internal or external.

Furthermore, using a hostname rather than a static IP address provides greater flexibility. If the IP address of the authentication service changes, updating the DNS record allows continued access without needing to change the configuration on the ProxySG. This approach is also beneficial for managing load balancing and failover strategies, as it can point to different servers behind a single hostname.

In contrast, while other options may seem plausible, they lack the essential characteristics that make using a hostname that can DNS-resolve to an IP address the most effective choice for virtual URL configuration in user authentication scenarios.