Token Validation

JSON Web Tokens (JWT) have become a cornerstone of modern web authentication and authorization systems. They provide a compact, URL-safe means of representing claims to be transferred between parties. However, the security of your application hinges on how you decode and validate these tokens. In this article, we’ll explore the process of securely parsing and verifying JWT tokens, ensuring your application remains protected against potential vulnerabilities. Visual Overview: graph LR subgraph JWT Token A[Header] --> B[Payload] --> C[Signature] end A --> D["{ alg: RS256, typ: JWT }"] B --> E["{ sub, iss, exp, iat, ... }"] C --> F["HMACSHA256(base64(header) + base64(payload), secret)"] style A fill:#667eea,color:#fff style B fill:#764ba2,color:#fff style C fill:#f093fb,color:#fff Understanding JWT Structure Before diving into decoding and validation, it’s essential to understand the structure of a JWT token. A JWT consists of three parts, separated by dots (.): ...

I’ve debugged hundreds of JWT validation bugs in production - most stem from skipping one critical step. JSON Web Tokens are the backbone of modern OAuth 2.0 auth, and getting validation right is non-negotiable. Visual Overview: sequenceDiagram participant User participant App as Client App participant AuthServer as Authorization Server participant Resource as Resource Server User->>App: 1. Click Login App->>AuthServer: 2. Authorization Request AuthServer->>User: 3. Login Page User->>AuthServer: 4. Authenticate AuthServer->>App: 5. Authorization Code App->>AuthServer: 6. Exchange Code for Token AuthServer->>App: 7. Access Token + Refresh Token App->>Resource: 8. API Request with Token Resource->>App: 9. Protected Resource Why This Matters According to OWASP’s API Security Top 10, broken authentication consistently ranks in the top 3 vulnerabilities. JWT validation is your first line of defense. Skip signature verification? You’re accepting forged tokens. Ignore expiration? Attackers replay stolen tokens indefinitely. ...