OAuth2 authorizes access and OIDC authenticates users. Learn their key differences and use cases

In the world of modern application security, OAuth2 and OpenID Connect (OIDC) play critical roles in authentication and authorization. While the two protocols often work hand-in-hand, they serve distinct purposes. Misunderstanding their differences can lead to implementation pitfalls, so let’s break it down in a straightforward way.

What is OAuth2?

OAuth2 is an authorization framework designed to allow third-party applications limited access to a resource on behalf of a user. It focuses on granting secure access to APIs without exposing user credentials, relying instead on tokens like access_token.

What is OpenID Connect?

OIDC, on the other hand, builds on top of OAuth2 and extends its functionality to include authentication. While OAuth2 answers the question, "Can this application access this resource?", OIDC answers, "Who is the user behind this access?"

OIDC introduces the id_token, a JSON Web Token (JWT) that contains claims about the user's identity. This makes it ideal for verifying user logins and retrieving user profile information.

Key Differences Between OAuth2 and OIDC

When to Use Access Token vs ID Token

The distinction between the two tokens is essential for correctly implementing OAuth2 and OIDC.

• Access Token: Used to call APIs on behalf of the user. Think of this as a pass granting limited rights to a third-party service.
• ID Token: Provides information about the user, such as their name, email, or other claims. This is used in the authentication flow, such as logging a user into an app.

When Should You Use OAuth2 or OIDC?

• OAuth2 Only: Use it when your application needs to access APIs or manage third-party integrations without requiring user identity details. For example, a service fetching data from another service’s API.
• OIDC with OAuth2: Use it when your application needs to authenticate users and retrieve identity information. For instance, enabling a "Login with Google" button or displaying user profiles in your app.

Closing Thoughts

OAuth2 and OIDC are complementary, each serving a specific role in the authentication and authorization ecosystem. By understanding their differences and appropriate use cases, you can design secure, user-friendly systems tailored to your application's needs. Whether you’re managing API access or creating seamless login experiences, choosing the right protocol and token is critical to building trust and functionality.

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