Which of the following Web authentication techniques uses a single sign-on scheme?

Basic authentication transmits Base64-encoded credentials per request and has no SSO mechanism - users must authenticate separately to each protected resource.

Digest authentication uses a challenge-response hash mechanism to avoid sending plaintext passwords but still requires per-resource authentication with no shared session or token federation.

NTLM authentication is a Windows challenge-response protocol for local network authentication that does not implement a cross-domain or cross-service SSO scheme in the way Passport does.

Microsoft Passport authentication is a centralized SSO service that authenticates users once via a trusted identity provider, issuing tokens that grant access to multiple participating sites and services. Unlike the other options, it is specifically architected around federated identity and token-based access delegation, which is the defining characteristic of SSO systems.