What describes a relationship where if resource A trusts resource B, and resource B trusts resource C, then resource A automatically trusts resource C?

The concept described in the question is known as transitive trust. This is a principle in which the trust is extended to third parties based on the established trust relationship between two parties. In this context, if resource A has established trust in resource B, and resource B has established trust in resource C, then it follows that resource A can also trust resource C. This type of trust model is often utilized in various access control systems and federated identity management, where the reliance on a chain of trust can simplify the authentication and authorization processes among multiple resources or domains.

In contrast, the other options listed refer to specific protocols or systems rather than to the general principle of trust relationships. SAML is a standard for exchanging authentication and authorization data between parties, primarily facilitating single sign-on. Shibboleth is an implementation that uses SAML for federated identity across organizations, focusing on web access management. OpenID is an authentication protocol that allows users to log in to multiple services without needing an account for each one, but does not describe a trust relationship mechanism as transitive trust does. Recognizing the distinction between these protocols and the concept of transitive trust is key to understanding this relationship in cybersecurity contexts.