OAuth2 and OpenID Connect (OIDC) are often mentioned together—and for good reason. They both deal with authorization and authentication, but they are not the same. Understanding the difference is key when designing secure systems in 2025.
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OAuth2: Authorization Framework
Purpose: Grants access to user resources without exposing credentials.
Use Case: "An app wants to access your Google Drive files."
How It Works: The app gets an access token from the authorization server, which it then uses to access the user's resources on the resource server.
Key Point: OAuth2 does not authenticate users—it only allows access to resources on their behalf.
Example Flow:
1. User grants permission.
2. App receives access token.
3. App uses token to access API (e.g., Google Drive).
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OpenID Connect (OIDC): Authentication Layer Built on OAuth2
Purpose: Verifies who the user is and provides identity information.
Use Case: "Log in with Google" button on a third-party app.
How It Works: Extends OAuth2 to return an ID token (JWT) containing user identity data (name, email, etc.).
Key Point: OIDC is for authentication—it tells you who the user is.
Example Flow:
1. User signs in via OpenID Provider (e.g., Google).
2. App receives access token + ID token.
3. App uses ID token to verify identity and log user in.
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Key Differences
Feature OAuth2 OpenID Connect
Main Purpose Authorization Authentication (and authorization)
Token Type Access Token Access Token + ID Token
User Identity Info Not included Included in ID Token (JWT)
Protocol Framework Protocol built on top of OAuth2
Use Case Example Accessing Google Calendar data Logging into apps with Google
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When to Use What?
Use OAuth2 when your app needs access to user data (e.g., Google Calendar, Dropbox).
Use OpenID Connect when your app needs to log users in and know who they are.
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Final Thought
Think of OAuth2 as a valet key—it lets apps open your car (access data) without knowing how to drive it (your identity). OIDC is the full key: it confirms your identity and lets apps interact securely.