The Web Security Appliance (WSA) supports different authentication protocols and schemes to acquire end-user credentials. The most common protocols are NTLMSSP and Kerberos, which are both supported by Active Directory realms. NTLMSSP is a challenge-response authentication protocol that uses a hash of the user's password to authenticate. Kerberos is a ticket-based authentication protocol that uses a trusted third-party (the Key Distribution Center) to issue tickets to the user and the service. Both protocols are more secure and widely supported than Basic authentication, which sends the user's credentials in clear text. CHAP, TACACS+, and RADIUS are not supported by the WSA for end-user authentication, although they can be used for external authentication of administrators or for credential encryption. References: 1, 2, 3
https://www.cisco.com/c/en/us/products/collateral/security/web-security-appliance/guide-c07-742373.html
https://frontegg.com/blog/authentication