A Comprehensive Guide to the Differences Between OAuth2 and OpenID Connect (OIDC): Key Considerations for Cognito and Auth0 Integration

🎯 Introduction: Clarifying the Basics of Authentication and Authorization

• OAuth2: A framework for granting access permissions on behalf of a user.
• OIDC (OpenID Connect): An identity layer built on top of OAuth2 that adds authentication capability—i.e., verifying “who” logged in.

Since services like Cognito and Auth0 support both, it’s crucial to design your implementation without confusion.

1. Comparing OAuth2 and OIDC

2. Why Separate the Two?

• OAuth2 alone is insecure for authentication
  It cannot determine if the access token belongs to the actual user—posing a serious security risk.

• OIDC includes “who is logged in” in a JWT
  ID Tokens provide secure claims like user ID or email.

In short: use OIDC for login functionality, and OAuth2 for external API access.

3. Support in Cognito and Auth0

🔹 AWS Cognito

• Supports various OAuth2 grant types: Auth Code, Implicit, Client Credentials.
• Supports OIDC for user authentication via ID tokens.
• Can also act as an OIDC provider and integrate with other IdPs like Auth0.

🔹 Auth0

• Supports both OAuth2 and OIDC with easy integration via GUI and SDKs.
• Flexible flow configuration (e.g., Auth Code + PKCE, Implicit).
• Can be used as an OIDC IdP for Cognito integration with SAML or Identity Pools.

4. Design Considerations and Common Pitfalls

1. Missing Scope Parameters

• You must include scope=openid to get an ID Token with OIDC.
• Add offline_access in Auth0 to receive a refresh token.

2. Token Format Differences

• Cognito issues JWTs for all token types (Access, Refresh, ID).
• Auth0 may issue opaque Access Tokens or fail to provide ID/Refresh tokens if scopes are misconfigured.

3. Integrating Cognito and Auth0

• When using Cognito as an “OIDC IdP”, the JWT structure (signature method, public key) must align with the IdP’s expectations.
• For Auth0 integration, use RS256 signed tokens, and ensure the correct Client ID and Audience are configured in Cognito.

4. Flow Selection Tips

• SPA or mobile apps: Use Authorization Code + PKCE for security.
• Backend-only apps: Standard Authorization Code flow works well.
• Machine-to-machine (M2M): Client Credentials grant is ideal, no ID Token needed, OAuth2 only.

5. Summary: Implementation and Operational Guidelines

✅ Recommended Flows by Use Case

🔍 Configuration Checklist

• [ ] Is scope=openid included?
• [ ] Are other necessary scopes like profile, email, offline_access set?
• [ ] Is RS256 signing and public key retrieval properly configured?
• [ ] Are appropriate security measures in place per flow (SPA, Mobile, Backend)?

Final Thoughts: Why Proper Separation Matters

• Confusing OAuth2 and OIDC can lead to implementations that lack true login verification—posing major security risks.
• Services like Auth0 and Cognito differ in token formats and scope behaviors; incorrect settings can lead to unexpected access failures in production.
• Use best practices to build a secure and scalable authentication and authorization foundation.

We hope this guide helps clarify the differences between OAuth2 and OIDC and aids in safely integrating Cognito and Auth0.
If you need specific flow examples or config files, feel free to reach out!