OAuth2OpenID

OAuth2OpenID is commonly understood as the combination of OAuth 2.0 and OpenID Connect, the latter providing an authentication layer on top of the OAuth 2.0 authorization framework. There is no separate standard formally named “OAuth2OpenID”; the widely adopted approach is OpenID Connect (OIDC), which uses OAuth 2.0 mechanisms to verify user identity and supply profile information.

OpenID Connect enables single sign-on and identity federation by issuing ID tokens, typically in JSON Web Token format, alongside traditional access tokens. The ID token carries claims about the authenticated user, such as a subject identifier, name, and email. Relying parties (clients) commonly request the openid scope to initiate authentication and may also request profile or email scopes for additional claims. The protocol also defines a userinfo endpoint to retrieve user attributes when needed.

Key components include an authorization server (identity provider), a resource server, and a client application. Discovery mechanisms provide endpoints and keys automatically, using a well-known configuration document. Public keys are exposed via a JWKS (JSON Web Key Set) for signature validation. Typical flows favor the Authorization Code flow with PKCE for both web and mobile clients, while the Implicit flow is discouraged in modern implementations due to security concerns.

Security best practices emphasize validating the ID token’s signature and claims (issuer, audience, expiration), using nonce values in authentication requests, enforcing HTTPS, and employing PKCE and short-lived tokens. OpenID Connect’s standardization of flows, scopes, and user information aims to deliver reliable authentication and user consent across diverse applications, with broad support from major identity providers.