Single Sign-On (SSO) allows users to authenticate once and access multiple applications without having to enter their credentials separately for each application. JWTs, or JSON Web Tokens, provide a secure way to implement SSO by exchanging authentication information between different applications.

In this article, we’ll discuss how to implement SSO using JWTs, including token generation, authentication, and verification.

What is a JWT?

A JSON Web Token (JWT) is a compact, URL-safe means of representing claims between two parties. It consists of three parts: a header, a payload, and a signature. The header contains information about the token, such as the hashing algorithm used for signing. The payload contains the claims or attributes of the user, while the signature ensures the integrity of the token.

Generating a JWT

To implement SSO with JWTs, the first step is to generate a token when a user logs in. This token should contain relevant information, such as the user’s ID and any necessary permissions. Here’s an example of how to generate a JWT using a library like jsonwebtoken in JavaScript:

const jwt = require('jsonwebtoken');

const generateToken = (userId, permissions) => {
  const payload = { userId, permissions };
  const secretKey = 'your-secret-key';

  const token = jwt.sign(payload, secretKey, { expiresIn: '1h' });

  return token;
};

In this example, we use the jsonwebtoken library to generate the token. The payload object contains the necessary data, while the secretKey is used to sign the token. The generated token is then returned.

Authenticating and Verifying a JWT

Once a user has a JWT, they can use it to authenticate and access protected resources in different applications. To achieve this, the application needs to verify the JWT’s signature and extract the user information from the payload. Here’s an example of how to authenticate and verify a JWT in a Node.js application:

const jwt = require('jsonwebtoken');

const authenticateToken = (token) => {
  const secretKey = 'your-secret-key';

  try {
    const payload = jwt.verify(token, secretKey);
    const { userId, permissions } = payload;

    // Add code to authenticate the user and provide access to resources

    return { userId, permissions };
  } catch (error) {
    throw new Error('Invalid token');
  }
};

In this example, we use the jsonwebtoken library to verify the token’s signature and extract the payload. If the token is valid, you can authenticate the user and provide access to the resources based on the extracted information. Otherwise, an error will be thrown.

Conclusion

Implementing Single Sign-On (SSO) with JSON Web Tokens (JWTs) provides a secure and efficient way to authenticate users across multiple applications. By generating a JWT upon login and verifying it on subsequent requests, you can enable SSO and improve the user experience.