OpenID Connect (OIDC) is an identity layer built on top of OAuth 2.0. OAuth 2.0 answers what a client may access; OIDC answers who the user or service is. It does this with signed identity information, usually an ID token, issued by an identity provider and verified by the application.
In cyber security, OIDC matters because it is a common foundation for single sign-on, federation, and delegated access in enterprise systems. Defenders use it to bind actions to a verified identity, enforce login and session controls, and separate authentication from authorization. Attackers often target weak implementations through token theft, redirect URI abuse, issuer or audience confusion, or flawed session handling. In agentic systems, OIDC helps prove which user or service is allowed to act, but it still must be paired with strict scopes, token validation, logging, and revocation controls.