In the world of modern web applications, secure authentication and authorization are crucial. Two widely used protocols that help achieve this are OAuth 2.0 and OpenID Connect (OIDC). While they are closely related and often used together, they serve different purposes. Understanding the distinction is key for developers, architects, and security professionals building secure and user-friendly systems.
What is OAuth 2.0?
OAuth 2.0 is an authorization framework that allows third-party applications to obtain limited access to a user's resources without exposing their credentials. Rather than dealing with authentication (verifying who the user is), OAuth 2.0 is focused on delegating access.
Key Features of OAuth 2.0
- Designed for authorization, not authentication.
- Enables access to protected resources via an access token.
- Allows users to grant limited access to their data on another service.
- Widely used for "Sign in with…" services (e.g., “Sign in with Google”), but only for authorization unless extended.
Common Use Case
Let’s say a user wants a calendar app to access their Google Calendar. OAuth 2.0 allows the calendar app to get a token from Google, granting it access to the user's calendar without sharing the user's password.
What is OpenID Connect?
OpenID Connect (OIDC) is an authentication layer built on top of OAuth 2.0. It allows clients to verify the identity of the user and obtain basic profile information in a standardized and secure way.
Key Features of OpenID Connect
- Adds authentication to OAuth 2.0.
- Introduces an ID token, which contains identity information about the user.
- Supports user login and single sign-on (SSO).
- Defines standard scopes such as openid, profile, email, etc.
Common Use Case
When a user logs in to an application using “Sign in with Google,” OpenID Connect allows the application to securely verify the user's identity and retrieve profile data (like name and email).
Key Differences at a Glance
| Feature |
OAuth 2.0 |
OpenID Connect |
| Purpose |
Authorization (granting access to resources) |
Authentication (verifying user identity) |
| Token Type |
Access Token |
Access Token + ID Token |
| Identity Info |
Not provided |
Provided via ID Token |
| Protocol Layer |
Framework |
The protocol layer on top of OAuth 2.0 |
| Used For |
Access delegation |
User login and SSO |
| Token Audience |
Resource server |
Client application |
How do They Work Together?
OpenID Connect extends OAuth 2.0, meaning that a system implementing OIDC also implements OAuth 2.0. When a user logs in via OIDC, the application receives both an ID token (for authentication) and an access token (for resource access). This dual capability allows developers to handle authentication and authorization seamlessly in a single flow.
Conclusion
While OAuth 2.0 and OpenID Connect are often used together, they serve distinct purposes. OAuth 2.0 provides the authorization framework, allowing apps to act on a user’s behalf. OpenID Connect builds on this by adding authentication, enabling applications to confirm the user's identity.
Understanding the difference helps ensure you're using the right tool for the job—whether that’s securely accessing a user’s data or confirming who they are.