Authentication Handbook: JWT & OAuth 2.0 Explained

This post provides a comprehensive guide to authentication concepts, focusing on JWT and OAuth 2.0, designed to clarify common misconceptions and prepare users for interview questions.

Key Concepts Covered:

• Authentication vs. Authorization: Distinguishing between verifying identity and granting permissions.
• Session-Based Authentication: Understanding traditional session management.
• Sessions vs. Tokens: Comparing stateful sessions with stateless tokens.
• Cookies: Their role in authentication and important security flags (HttpOnly, Secure, SameSite).
• JWT (JSON Web Token):
  • Fundamentals: Structure of a JWT (Header, Payload, Signature).
  • Claims: Standard claims like sub (subject), iss (issuer), aud (audience), iat (issued at), exp (expiration).
  • Encoding vs. Encryption: Understanding the difference.
  • Creation & Verification: The process of generating and validating JWTs.
  • Complete Flow: The end-to-end process of JWT authentication.
  • Access Token vs. Refresh Token: Their distinct purposes and lifecycles.
  • Token Expiration Strategy: Managing token expiry effectively.
  • Refresh Token Rotation: A security best practice to mitigate risks.
  • Refresh Token Reuse Detection: Preventing unauthorized token usage.
  • Logout & Token Revocation: Strategies for invalidating tokens.
  • JWT Storage: Where to securely store JWTs (e.g., HttpOnly + Secure + SameSite cookies).
• Security Risks: Understanding XSS (Cross-Site Scripting) and CSRF (Cross-Site Request Forgery).
• OAuth 2.0:
  • Fundamentals: The core components: Resource Owner, Client, Authorization Server, Resource Server.
  • Scopes & Consent: How permissions are managed.
  • Authorization Code Flow: A common and secure flow.
  • PKCE (Proof Key for Code Exchange): An enhancement for the Authorization Code Flow, especially for public clients.
• Comparisons:
  • OAuth vs. JWT vs. Sessions: Clarifying their relationships and differences.
  • Common Misconception: OAuth 2.0 is primarily an authorization framework, not an authentication protocol. OpenID Connect (OIDC) is often used on top of OAuth 2.0 for identity/login.
  • JWT vs. OAuth: JWT is a token format; OAuth can use JWTs but doesn't require them.

Interview Question Focus:

• Revoking Stateless JWTs: Addressing the challenge of immediate revocation for stateless JWTs. Common solutions include:
  • Short-lived Access Tokens.
  • Refresh Token Rotation.
  • Revocation/Denylist mechanisms when immediate revocation is critical.

Security Best Practices:

• Use HTTPS for all communications.
• Implement short-lived Access Tokens (e.g., minutes).
• Use Refresh Token Rotation.
• Implement Refresh Token Reuse Detection.
• Validate all tokens rigorously.
• Store tokens securely: Prefer HttpOnly, Secure, and SameSite cookies for sensitive tokens. Avoid localStorage or sessionStorage for critical tokens due to XSS risks.
• Implement token revocation mechanisms when necessary.
• Apply the principle of least privilege.
• Protect against common security threats like XSS, CSRF, replay attacks, token tampering, and brute force attacks.

Common Authentication Vulnerabilities:

• XSS (Cross-Site Scripting)
• CSRF (Cross-Site Request Forgery)
• Replay Attacks
• Token Tampering
• Brute Force Attacks

Real-world Architecture Insights:

• The handbook includes diagrams and explanations of real-world authentication architectures.