Introduction

OpenID Connect (OIDC) is a modern authentication protocol built on top of OAuth 2.0. It enables secure identity verification and user information exchange between a Client (Application) and an Identity Provider (IdP).

OIDC is widely used in web and mobile apps to support Single Sign-On (SSO), especially with providers like Google, Microsoft, Okta, and Auth0.

🧭 Step-by-Step Breakdown: Authorization Code Flow

1. User Attempts to Log In

• The user visits your website and clicks “Log in.”
• The website (acting as the OIDC Client) initiates authentication by redirecting the user to the Identity Provider (IdP).

2. Redirect to Authorization Endpoint

• The client constructs a URL pointing to the IdP’s authorization endpoint, including:
  • client_id
  • redirect_uri
  • response_type=code
  • scope=openid (plus optional: profile, email)
  • state and nonce for security
• The user is redirected to this URL in their browser.

3. User Authenticates at the IdP

• The IdP displays a login prompt (e.g., username/password, MFA).
• Once authenticated, the IdP redirects the user back to the client via the redirect_uri, including:
  • An authorization code
  • The state parameter for CSRF protection

4. Client Exchanges Code for Tokens

• The client sends a POST request to the token endpoint of the IdP with:
  • The authorization code
  • client_id and client_secret (or private key for confidential clients)
  • redirect_uri
  • grant_type=authorization_code
• The IdP responds with:
  • ID Token (JWT with user identity)
  • Access Token (for accessing APIs)
  • Optionally, a Refresh Token

5. ID Token Validation

• The client validates the ID Token, checking:
  • Signature (using IdP’s public key)
  • Issuer (iss)
  • Audience (aud)
  • Nonce
  • Expiration (exp)
• If valid, the user is authenticated.

6. User Session Established

• The client creates a local session (e.g., cookie or JWT).
• The user is now logged in and redirected to the original or dashboard page.

🔐 Key Components

✅ Benefits of OIDC Authorization Code Flow

• 🔐 Strong Security — Server-side token exchange avoids exposing tokens in the browser
• 🌐 SSO-Friendly — Works across apps with federated IdPs
• 📦 Rich Identity Data — Access user profile, email, and more
• 🔁 Refresh Tokens — Maintain sessions without re-authentication
• 🧰 OAuth-Compatible — Easily integrate with OAuth-protected APIs

🔚 Conclusion

OIDC’s Authorization Code Flow is the gold standard for secure, standards-based authentication in web applications. It offers strong security, flexibility, and compatibility with leading identity providers.

For more identity & access security tutorials, visit IDAMworks.com.