OpenID Connect (OIDC)
An identity layer built on top of OAuth 2.0 that adds a standardized way to prove who the user is — the "login" OAuth alone was never designed to provide.
aka: OIDC
OIDC reuses OAuth’s flows and roles but adds the ID token — a JWT full of claims about the user — plus discovery, a JWKS endpoint for key rotation, and a UserInfo endpoint. It exists because a raw OAuth access token proves permission, not identity, and enough people misused it as a login mechanism that the ecosystem needed a real one.