What is the difference between OAuth2 and OpenID Connect?

OAuth2 is fundamentally an AUTHORIZATION framework — it grants delegated access to resources but doesn't formally define how to establish user identity. OpenID Connect is a thin identity layer built on top of OAuth2 that standardizes AUTHENTICATION, introducing the JWT-based ID Token, the 'openid' scope, and a /userinfo endpoint — 'Sign in with Google' is an OIDC flow riding on top of OAuth2's Authorization Code grant.