Key auth protocols:
Kerberos (Windows AD, ticket-based),
RADIUS (network access — Wi-Fi, VPN),
TACACS+ (Cisco device admin),
LDAP/SAML (enterprise SSO),
EAP (extensible framework for 802.1X).
RADIUS encrypts only password. TACACS+ encrypts entire payload (more secure for device admin). Kerberos uses tickets, not passwords over the network. SAML for web SSO. RADIUS for 802.1X wireless/VPN authentication. Know when to use each protocol.