Introduction to JWT (JSON Web Token) and Verification Mechanism

What is JWT (JSON Web Token)?

JWT (JSON Web Token) is an open standard (RFC 7519) for securely transferring information between two parties as a JSON object. It is widely used for authentication and information exchange due to its compact and self-contained structure.

Structure of JWT

A JWT consists of three parts separated by dots (.):

1. Header: Contains the type of token (JWT) and the signing algorithm (e.g., HS256, RS256).
2. Payload: Contains the claims (information about the user or metadata like expiration time).
3. Signature: Created by signing the encoded header and payload with a secret or key to ensure data integrity.

Common Use Cases

• Authentication: Once a user logs in, subsequent requests include the JWT, allowing access to routes and resources permitted with that token.
• Information Exchange: JWTs are a secure way to transmit data because they can be signed and verified.

Security Best Practices

• Don’t store sensitive data: The payload is Base64Url encoded, not encrypted. Anyone can decode it.
• Use strong algorithms: Prefer RS256 (asymmetric) over HS256 (symmetric) for better security in distributed systems.
• Set short expiration times: Minimize the window of risk if a token is stolen.
• Verify the Signature: Always verify the token on the server side before trusting the data.

Debugging JWT

When a JWT fails verification, check the following:

• Has the token expired (exp claim)?
• Is the signature valid for the provided public/secret key?
• Are the claims like iss (issuer) or aud (audience) correct?

Using a JWT Debugger tool can help you inspect the content and test signatures easily.