JWT (JSON Web Token) is a compact and self-contained way for securely transmitting information between parties as a JSON object. It’s widely used for authentication and authorization in modern web applications.

Key Components of JWT

1. Header:
   • Contains two parts: the type of token (JWT) and the signing algorithm being used (e.g., HMAC SHA256).
2. Payload:
   • Includes the claims, which are statements about an entity (typically the user) and additional data.
   • Types of claims:
     • Registered Claims: Predefined claims like iss (issuer), exp (expiration time), sub (subject), and aud (audience).
     • Public Claims: Claims defined by the users of the JWT.
     • Private Claims: Custom claims created to share information between parties that agree on using them.
3. Signature:
   • Ensures the token’s integrity by verifying that the token hasn’t been altered after it was signed.
   • Created by encoding the header and payload and signing them using a secret key.

How JWT Works in Spring Boot

1. User Authentication:
   • Upon logging in, the server authenticates the user. If successful, the server generates a JWT token containing information about the user’s identity and other claims.
2. Token Distribution:
   • The JWT token is sent to the client and typically stored in local storage or a cookie.
3. Token Usage:
   • For each subsequent request, the client includes the JWT token in the Authorization header (Bearer <token>).
4. Token Verification:
   • The server verifies the token’s signature and claims. If valid, the server processes the request; otherwise, it rejects the request.

Benefits of Using JWT

• Stateless: No need to store session information on the server, as the token itself contains all the necessary data.
• Scalable: Since JWT is stateless, it can be easily used in distributed systems.
• Compact: JWTs are compact and can be easily transmitted in URLs, POST parameters, or inside headers.
• Secure: When properly signed and verified, JWTs ensure data integrity and authenticity.

Common Use Cases

• Authentication: Verify the identity of users.
• Authorization: Provide access control by including user roles and permissions within the token.
• Information Exchange: Securely transmit information between parties.

By leveraging JWT in a Spring Boot application, you can create a robust and secure system for handling user authentication and authorization, ensuring that your application is both efficient and scalable.
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