What is OAuth 2.0, and what is OpenID Connect?

OAuth 2.0 is an open authorisation protocol that lets third-party applications access resources on a user's behalf without exposing the user's authentication data, using access tokens issued by an authorization server; OpenID Connect (OIDC) is an open authentication standard built on top of OAuth 2.0.

* The OAuth 2.0 roles and the ID token that OpenID Connect adds. *

The slogan: OAuth is about delegated access, OIDC adds who the user is (the ID token). Defined in RFC 6749 and the OpenID Connect Core specification.

Go deeper:

• RFC 6749 OAuth 2.0 Authorization Framework — roles, grant types and tokens as standardised.
• OpenID Connect Core 1.0 — the identity layer on OAuth 2.0 and the ID token.
• OpenID Connect (Wikipedia) — the ID token as the assertion of an OAuth-based login.