EAP-FAST, also known as Flexible Authentication via Secure Tunneling, is an EAP (Extensible Authentication Protocol) developed by Cisco. It is used in wireless networks and point-to-point connections to perform session authentication. Its purpose is to replace the LEAP (lightweight extensible authentication protocol).
LEAP, also developed by Cisco, was widely adopted as a wireless authentication protocol but contains known security vulnerabilities, especially when used with weak passwords. EAP-FAST addresses these vulnerabilities by performing authentication over a TLS (Transport Layer Security) tunnel, which is established using a PAC (Protected Access Credential).