OAuth 2.0 and OpenID Connect (OIDC) are two fundamental protocols in the world of authentication and authorization. While they often go hand in hand, they serve distinct purposes and are not interchangeable. This blog post will delve into the differences between OAuth 2.0 and OIDC, clarify their roles, and help you determine when to use each.

What is OAuth 2.0?

OAuth 2.0 is an authorization framework that enables applications to access resources on behalf of a user without sharing the user’s credentials. It’s designed to provide a secure and flexible way for third-party applications to access user data stored on a server, such as emails, photos, or calendar events.

Core Concepts of OAuth 2.0

  • Authorization Grant: A method used by the resource owner to grant access to a protected resource. OAuth 2.0 defines several grant types, including:

    • Authorization Code: Used for web applications.
    • Implicit: Used for browser-based applications.
    • Resource Owner Password Credentials: Used for trusted applications.
    • Client Credentials: Used for applications that need to access resources on their own behalf.

  • Access Token: A short-lived token issued by the authorization server. It is used by the client to access protected resources.

  • Refresh Token: A token that can be used to obtain a new access token after the current one has expired.

OAuth 2.0 Use Case: Accessing User Data

Imagine you’re building a web application that needs to access a user’s Google Calendar. Using OAuth 2.0, the user can grant your application permission to access their calendar without sharing their Google password. The authorization server (Google) issues an access token, which your application uses to make API requests to Google’s servers.

What is OpenID Connect (OIDC)?

OIDC is built on top of OAuth 2.0 and adds an authentication layer. While OAuth 2.0 focuses on authorization, OIDC is specifically designed to authenticate users and provide their identity information. It enables single sign-on (SSO) across multiple applications and services.

OIDC Core Concepts

  • Identity Token: A JSON Web Token (JWT) that contains user claims, such as username, email, and other profile information.

  • Authentication Endpoint: The endpoint where the user authenticates and consents to share their identity information.

  • UserInfo Endpoint: An optional endpoint that provides additional user information.

OIDC Use Case: User Authentication

Consider a scenario where you want to implement SSO across multiple applications. Using OIDC, users can log in once and access multiple applications without re-entering their credentials. For example, logging in to your company’s intranet using your corporate email and password allows you to access other services like the cloud storage or project management tool without logging in again.

Key Differences Between OAuth 2.0 and OIDC

Feature OAuth 2.0 OIDC
Primary Function Authorization (access control) Authentication (user identification)
Token Type Access Token (for resource access) Identity Token (for user authentication)
Scope Grants access to specific resources Provides user identity information
Use Case Accessing user data (e.g., Google Calendar, Facebook photos) Authenticating users and enabling SSO across applications
Protocol Focuses on resource access Built on top of OAuth 2.0 to add authentication capabilities

Do You Need OIDC for Login?

The answer depends on your use case:

  • If you need only authorization (access to resources): OAuth 2.0 alone might suffice. For example, if your application needs to access a user’s email or photos, OAuth 2.0 can handle the authorization process.

  • If you need authentication (user identification): OIDC is the way to go. OIDC not only handles authorization but also provides user identity information, making it ideal for scenarios where you need to authenticate users and manage their sessions across multiple applications.

Real-World Example: Implementing Login with OIDC

Suppose you’re building a web application that allows users to log in using their Google account. By integrating OIDC, you can:

  1. Redirect users to Google’s authentication page.
  2. After successful authentication, Google (the identity provider) returns an identity token to your application.
  3. Your application can then verify the token and retrieve user information like their email, name, and profile picture.

Implementation Considerations

OAuth 2.0 Implementation

If you’re using OAuth 2.0 for resource access, you’ll typically follow the Authorization Code Flow:

  1. Redirect to Authorization Server: Your application redirects the user to the authorization server (e.g., Google) with a request for an authorization code.
  2. User Grants Permission: The user logs in and grants permission for your application to access their data.
  3. Authorization Code Issued: The authorization server issues an authorization code to your application.
  4. Exchange Code for Tokens: Your application exchanges the authorization code for an access token and, optionally, a refresh token.
  5. Access Protected Resources: Use the access token to make API requests to the resource server.

Code Example (OAuth 2.0 Authorization Code Flow):

import requests

# Step 1: Redirect to authorization server
redirect_uri = "https://your-app.com/callback"
auth_url = f"https://auth-server.com/authorize?client_id=CLIENT_ID&redirect_uri={redirect_uri}&response_type=code"

# Step 2: User grants permission and authorization server redirects back with code
code = "AUTHORIZATION_CODE"

# Step 3: Exchange code for tokens
token_url = "https://auth-server.com/token"
data = {
    "client_id