OpenID Connect — Complete Identity Authentication Guide

In this tutorial, you will learn about Openid Connect. We cover key concepts, practical examples, and best practices to help you master this topic.

OpenID Connect (OIDC) is an identity layer on top of OAuth 2.0. It adds an ID token (a JWT containing user identity claims) and a UserInfo endpoint, enabling standardized user authentication.

What You'll Learn

You'll learn how OIDC extends OAuth 2.0, ID token structure, and how to implement OIDC login.

Why It Matters

OIDC is the industry standard for user authentication, used by Google, Microsoft, Apple, and most identity providers. It eliminates the need to build custom login systems.

Real-World Use

A corporate intranet uses OIDC with Azure AD. Employees sign in once and access all internal tools (email, calendar, CRM). When an employee leaves, disabling their AD account immediately revokes access everywhere.

sequenceDiagram
    participant User
    participant App
    participant IDP as Identity Provider
    User->>App: Click "Sign In"
    App->>IDP: Auth Request (scope=openid profile)
    IDP->>User: Login
    User->>IDP: Credentials
    IDP->>App: ID Token + Access Token
    App->>App: Validate ID Token (signature, claims)
    App->>User: Authenticated

Implementation

import jwt
import requests
from authlib.integrations.flask_client import OAuth

oauth = OAuth()
oauth.register(
    name="google",
    client_id="your-client-id",
    client_secret="your-client-secret",
    server_metadata_url="https://accounts.google.com/.well-known/openid-configuration",
    client_kwargs={"scope": "openid profile email"}
)

def get_user_info(token):
    id_token = token.get("id_token")
    claims = oauth.google.parse_id_token(token)
    user_info = requests.get(
        "https://openidconnect.googleapis.com/v1/userinfo",
        headers={"Authorization": f"Bearer {token['access_token']}"}
    ).json()
    return claims, user_info

# Manual ID token validation
def validate_id_token(id_token):
    try:
        header = jwt.get_unverified_header(id_token)
        jwks = requests.get("https://auth.example.com/.well-known/jwks.json").json()
        signing_key = None
        for key in jwks["keys"]:
            if key["kid"] == header["kid"]:
                from jwt import PyJWK
                signing_key = PyJWK(key).key
        claims = jwt.decode(
            id_token,
            signing_key,
            algorithms=["RS256"],
            audience="your-client-id",
            issuer="https://auth.example.com",
            options={"require": ["iss", "sub", "aud", "exp", "iat"]}
        )
        return claims
    except Exception as e:
        raise ValueError(f"Invalid ID token: {e}")

Common Mistakes

Practice Questions

1. What is the difference between ID token and access token?
2. What claims are required in an ID token?
3. How does OIDC enable single sign-on?
4. What is the UserInfo endpoint?
5. What is the nonce parameter?

Challenge

Implement OIDC login with a provider (Google, Auth0, or Keycloak). Validate the ID token manually. Extract user profile and create a local session.

What's Next

Learn about SAML for enterprise identity federation.