Which protocol enables different websites to utilize a trusted third party for user authentication?

The correct answer, Open Authorization (OAuth), is a widely used protocol that allows different websites and applications to delegate user authentication to a trusted third-party service. OAuth enables users to give limited access to their resources on one site to another site without sharing their credentials, such as usernames and passwords. By using OAuth, a user can log in to a service using their account from a trusted provider (e.g., Google or Facebook), and the service will receive a token that validates the user's identity and access permissions.

This delegation of authentication is particularly valuable in scenarios where users frequently access multiple applications, as it simplifies the login process by allowing single sign-on capabilities. Users can authenticate once through the trusted provider and gain access to multiple services without needing to manage separate credentials for each one.

While other options listed also involve authentication and authorization, they serve distinct purposes. OpenID focuses directly on user authentication rather than authorization, SAML is primarily used for exchanging authentication and authorization data between parties (often in enterprise environments), and JSON Web Token is used to represent claims securely but does not specifically define how services can authenticate users across different platforms. Thus, OAuth stands out as the protocol specifically designed for utilizing a trusted third party for user authentication across various websites.