Return to topic cards

JSON Web Tokens (JWT) for Secure Authentication

JWT StructureSigning AlgorithmsSecurity Best PracticesToken Lifecycle ManagementReal-World Applications

JSON Web Tokens (JWTs) are a compact, URL-safe means of representing claims to be transferred between two parties. They are used for securely transmitting information as a JSON object, commonly used for authentication and authorization.

Key Points

  • Structure: JWTs consist of three parts: Header, Payload, and Signature, each Base64Url encoded and separated by dots.
  • Header: Specifies the token type and signing algorithm.
  • Payload: Contains claims, which are statements about an entity (e.g., user) and additional data.
  • Signature: Ensures the token's integrity and authenticity by verifying it hasn't been altered.
  • Signing Algorithms: Include symmetric (HMAC) and asymmetric (RSA or ECDSA) methods.

Detailed Explanation

Structure

JWTs consist of three parts:

  1. Header: Specifies the token type and signing algorithm.
  2. Payload: Contains claims, which are statements about an entity (e.g., user) and additional data.
  3. Signature: Ensures the token's integrity and authenticity by verifying it hasn't been altered.

Signing Algorithms

Signing algorithms include:

  • Symmetric (HMAC): Uses a shared secret key.
  • Asymmetric (RSA or ECDSA): Uses a pair of public and private keys.

Practical Example

Header: {"alg": "HS256", "typ": "JWT"}
Payload: {"sub": "1234567890", "name": "John Doe", "iat": 1516239022}
Signature: HMACSHA256(base64UrlEncode(header) + "." + base64UrlEncode(payload), secret)

Real-World Application

JWTs are widely used in web applications for stateless authentication. For example, when a user logs in, the server generates a JWT and sends it to the client. The client stores this token and includes it in the Authorization header of subsequent requests to access protected resources.

Key Takeaways

  • Always verify the token's signature to ensure it hasn't been tampered with.
  • Avoid storing sensitive information in the payload as it can be decoded.
  • Choose appropriate token lifetimes based on the application's security requirements.

Learn More

  • JWT.io: A comprehensive resource for understanding and implementing JWTs.