Unlocking the Power of JSON Web Tokens in Authentication

The Rise of JWT in Modern Applications

In today’s fast-paced digital landscape, authentication has become a critical component of any successful project. As a developer, implementing JSON Web Tokens (JWT) in a MERN stack application has become a crucial task.

What is JWT?

JWT is an open, industry-standard method for securely representing claims between two parties. A JWT consists of a header, payload, and signature, making it a safe way to transmit information between services. In simple terms, a JWT is a string in a specific format, which can be easily verified and validated.

The JWT Flow

In a microservice-based architecture, we have multiple services, including an Authentication Service. This service retrieves a user claim based on a reference token in a domain cookie and generates a JWT for this claim. If a valid JWT is returned, the call is forwarded to the corresponding service, and the JWT is passed in the request header as an OAuth bearer token for further authorization.

Getting Started with JWT in React

To begin, you’ll need:

• Node.js (latest LTS version)
• Visual Studio Code (with React extensions)
• Google Chrome with React DevTools extension
• A good terminal, like iTerm2 (macOS)

Generating JWT on the Server

To generate a JWT, we need to choose a library that supports the recommended algorithms HS512 and RS512. We’ll use jsrsasign, which supports all the necessary algorithms.

const headers = {
  alg: 'HS512',
  typ: 'JWT'
};

const claims = {
  user: 'username',
  role: 'admin'
};

const privateKey = 'your_secret_private_key';

Implementing the Encoding Function

We’ll create a claims object with the necessary user information, then generate a private key. Note that the private key should be kept secret and not used in client-side code.

const token = KJUR.jws.JWS.sign(headers.alg, headers.typ, claims, privateKey);
console.log(token);

Decoding and Validating JWT

To validate the token, we need to verify that it was signed with the same private key. We’ll implement a validation function using the JSRSASign.jws.JWS.verifyJWT() function.

const isValid = KJUR.jws.JWS.verifyJWT(token, privateKey);
if (isValid) {
  console.log('Token is valid');
} else {
  console.log('Token is invalid');
}

Decoding the Token

Once validated, we can decode the token to access the payload securely. We’ll split the token, parse the header and claims, and log the output.

const decodedToken = token.split('.');
const header = JSON.parse(atob(decodedToken[0]));
const claims = JSON.parse(atob(decodedToken[1]));
console.log(header);
console.log(claims);

Complete Code and Next Steps

Here’s the complete code for signing, generating, validating, verifying, and decoding a JWT. In the next part, we’ll explore building REST API endpoints for the client to consume.