OpenID Connect (OIDC)
Also known as: OpenID Connect · OpenIDC
Definition
OpenID Connect (OIDC) is an authentication protocol built on top of OAuth 2.0/2.1 that adds an ID Token (a signed JWT) carrying claims about the authenticated user.
OIDC adds the missing authentication layer to OAuth's authorization framework. Where OAuth answers "can this client access this resource?", OIDC answers "who is this user?". Implementations expose a discovery document at `/.well-known/openid-configuration` declaring endpoints, supported algorithms, and key sets.
The ID Token is a JWT signed by the OP (OpenID Provider). The relying party (client) validates the signature against the OP's JWKS, checks issuer + audience + expiration + nonce, and extracts claims like `sub` (user ID), `email`, `groups`, etc. Modern federated login (Sign in with Google, Microsoft, Apple) is OIDC.