About JWT Tokens
JSON Web Tokens (JWT) are an open standard for securely transmitting information between parties as a JSON object. JWTs consist of three parts separated by dots: header, payload, and signature. The header and payload are Base64URL encoded, making them easy to decode and inspect.
JWT Structure
- Header: Contains token type and signing algorithm (e.g., HS256, RS256)
- Payload: Contains claims (user data, expiration, etc.)
- Signature: Used to verify token authenticity and integrity
Common Use Cases
- Authentication: Verify user identity in web applications
- API Authorization: Authorize API requests
- Session Management: Manage user sessions without server-side storage
- Information Exchange: Securely transmit information between parties
- Single Sign-On (SSO): Enable SSO across multiple applications
Common JWT Claims
- iss (issuer): Who issued the token
- sub (subject): Who the token is about
- exp (expiration): When the token expires
- iat (issued at): When the token was issued
- aud (audience): Who the token is intended for
Security Best Practices
- Never store sensitive data in JWT payloads (they can be decoded)
- Always verify the signature before trusting a JWT
- Use HTTPS to prevent token interception
- Set appropriate expiration times for tokens
- Use strong signing algorithms (RS256, ES256) for production
- Validate all claims, especially expiration
