OAuth vs OpenID: Understanding the Key Differences

OAuth and OpenID Connect (OIDC) are protocols that developers often confuse due to their overlapping features. OAuth is an authorization framework that allows apps to access resources on behalf of a user without exposing their credentials, while OIDC is an authentication protocol built on top of OAuth 2.0 that combines resource sharing and authentication. OAuth is useful when you only need to authorize access to resources without verifying the user's identity, whereas OIDC is appropriate when you need both authorization and authentication. ID tokens in OIDC contain user profile information, while access tokens grant apps permission to access resources on behalf of the user. OAuth addresses security flaws by using access tokens instead of usernames and passwords, enabling multiple flows for different types of apps, and providing fine-grained access control. However, it has a steep learning curve, lacks interoperability between providers, and poses security risks if tokens are stolen. OIDC enables Single Sign-On (SSO) authentication, reduces sign-up friction, and offloads authentication to third-party providers. When using OAuth and OIDC together, OIDC is used for SSO authentication, while OAuth controls access to protected resources once the user is authenticated.