Final answer:
The WLAN security approach that requires user authentication against a server's database is 802.1X, often paired with WPA/WPA2 Enterprise modes. WEP, WPA2 with PSK, and MAC filtering do not require an authentication server and instead use other security mechanisms.
Step-by-step explanation:
The approach to wireless LAN (WLAN) security that requires users to authenticate against an authentication server's database, as opposed to configuring a client with a Pre-Shared Key (PSK), is c) 802.1X. This security protocol provides an authentication framework for wireless LANs, allowing users to be authenticated by a central authority. The other options, such as WEP (Wired Equivalent Privacy) and WPA2 (Wi-Fi Protected Access 2) with a PSK, involve different security mechanisms. WEP is an outdated and less secure protocol, whereas WPA2 with a PSK does not require an authentication server but rather uses a shared key amongst users. MAC filtering is a method to control access based on the hardware address but does not involve an authentication server.
802.1X authentication is often used in conjunction with other security protocols like WPA or WPA2, in a configuration known as WPA-Enterprise or WPA2-Enterprise. This enterprise mode operates in contrast to WPA-Personal or WPA2-Personal, where a PSK is used.