Your customer is using PSK as their only authentication.

EAP-TLS (Extensible Authentication Protocol - Transport Layer Security) is the most secure EAP type that utilizes certificates for mutual authentication between the client and the server.In this method, both the client and the server present certificates to authenticate each other, eliminating the need for passwords and providing strong security against various attacks.

The CWDP-305 Official Study and Reference Guide emphasizes the importance of using EAP-TLS in environments where strong security is required:

"EAP-TLS is considered one of the most secure EAP types because it uses certificates for both client and server authentication. It provides mutual authentication and is widely supported."

Therefore, for organizations seeking to enhance their WLAN security by moving away from PSK and implementing certificate-based authentication, EAP-TLS is the recommended choice.