Single Sign-On and Federated Identity
SSO technologies
- Kerberos — symmetric-key SSO using a KDC with an authentication service and ticket granting service. Tickets are time-stamped, so clock skew breaks it and the KDC is a single point of failure.
- LDAP / directory services — the identity store queried for authentication and attributes.
- RADIUS, TACACS+, and Diameter — AAA protocols; TACACS+ encrypts the full payload and separates authentication, authorization, and accounting.
Federation
Federated identity lets a user authenticate at their home identity provider and access resources at a separate service provider without a second account. SAML carries assertions between the identity provider and service provider; OAuth 2.0 grants delegated authorization; OpenID Connect adds an identity layer on top of OAuth.
SSO trade-off
SSO improves usability and reduces password fatigue, but it concentrates risk: one compromised credential opens every connected system. Pair SSO with strong multifactor authentication.