OIDC Authentication Flow: A Visual Guide with Examples

OpenID Connect is an identity layer built on top of OAuth 2.0 that provides a standardized way for apps to verify a user’s identity and obtain basic profile information. It allows applications to authenticate users without handling passwords, leveraging the authentication capabilities of existing providers like Google, Microsoft, and others.

What is OpenID Connect?

OpenID Connect is an open standard for authentication that extends OAuth 2.0 to provide user information through a secure, reliable, and interoperable mechanism. It uses JSON Web Tokens (JWT) to encode user claims and ensures that the identity provider (IdP) has authenticated the user.

Why use OpenID Connect?

Use OpenID Connect when:

• You need a standardized way to authenticate users across different platforms.
• You want to leverage existing identity providers for authentication.
• You require a secure method to obtain user profile information.

What are the components of an OIDC flow?

The key components of an OIDC flow include:

• Client: The application requesting user authentication.
• Authorization Server: The IdP that authenticates the user and issues tokens.
• User: The entity being authenticated.
• Tokens: Credentials issued by the Authorization Server, including the ID Token and Access Token.

What is the authorization code flow in OIDC?

The authorization code flow is the most common OIDC flow used for web applications. It involves several steps to ensure secure authentication and authorization.

Step-by-step guide

Example flow

Here’s a simplified example of the authorization code flow:

1. Register your application

   # Example registration details
   CLIENT_ID="your-client-id"
   CLIENT_SECRET="your-client-secret"
   REDIRECT_URI="https://yourapp.com/callback"
   AUTHORIZATION_ENDPOINT="https://idp.example.com/auth"
   TOKEN_ENDPOINT="https://idp.example.com/token"
   

2. Redirect to the authorization endpoint

   # Construct the authorization URL
   AUTH_URL="$AUTHORIZATION_ENDPOINT?response_type=code&client_id=$CLIENT_ID&redirect_uri=$REDIRECT_URI&scope=openid%20profile&state=random_state_string"
   echo $AUTH_URL
   

3. User authenticates The user visits the constructed URL, logs in, and grants consent.

4. Receive the authorization code

   # Example callback URL received by your app
   CALLBACK_URL="https://yourapp.com/callback?code=AUTHORIZATION_CODE&state=random_state_string"
   

5. Exchange the authorization code for tokens

   # Send a POST request to the token endpoint
   curl -X POST $TOKEN_ENDPOINT \
   -d "grant_type=authorization_code" \
   -d "code=AUTHORIZATION_CODE" \
   -d "redirect_uri=$REDIRECT_URI" \
   -d "client_id=$CLIENT_ID" \
   -d "client_secret=$CLIENT_SECRET"
   

6. Validate the ID Token

   # Example ID Token response
   ID_TOKEN="eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c"
   
   # Validate the token using a library or custom logic
   # Example using jwt.io or a JWT library in your programming language
   

How do you handle errors in OIDC?

Handling errors is crucial for a smooth user experience and robust application security.

Common errors

• Invalid request: Missing or malformed parameters.
• Unauthorized client: Invalid client ID or secret.
• Access denied: User declined authorization.
• Unsupported response type: Requested response type is not supported.
• Invalid scope: Requested scope is invalid, unknown, or malformed.
• Server error: The authorization server encountered an unexpected condition.
• Temporarily unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.

Example error handling

Here’s how you might handle an “invalid request” error:

# Example error response from token endpoint
ERROR_RESPONSE='{"error":"invalid_request","error_description":"Missing parameter: redirect_uri"}'

# Handle the error in your application logic
if [[ $ERROR_RESPONSE == *"invalid_request"* ]]; then
  echo "Error: Missing redirect URI. Please check your request parameters."
fi

What are the security considerations for OIDC?

Security is paramount in any authentication flow. Here are some critical considerations for implementing OIDC securely.

Secure client secrets

Validate ID tokens

Always validate the ID token’s signature and claims to ensure it’s genuine and hasn’t been tampered with.

Use HTTPS

Ensure all communications between your app, the IdP, and the user are encrypted using HTTPS.

Protect against CSRF

Implement Cross-Site Request Forgery (CSRF) protection by using state parameters and validating them.

Implement token revocation

Provide a mechanism for token revocation in case of security incidents.

Monitor and audit

Regularly monitor and audit your authentication flows for suspicious activity.

How does OIDC compare to SAML?

Quick reference

OIDC pitfalls to avoid

Avoid these common pitfalls to ensure a secure and reliable OIDC implementation.

Incorrect token validation

Exposing client secrets

Ignoring CSRF protection

Not monitoring token usage

Misconfiguring redirect URIs

Conclusion

Implementing OpenID Connect authentication flow requires careful attention to detail and adherence to best practices. By following the steps outlined in this guide, you can create a secure and efficient authentication mechanism for your applications. Remember to validate tokens, keep client secrets secure, and monitor your implementation for potential security issues. That’s it. Simple, secure, works.