Authentication in MERN Stack Using JWT

 User authentication is a critical part of most web applications. In the MERN stack—MongoDB, Express.js, React, and Node.js—you can implement secure authentication using JSON Web Tokens (JWT). JWT provides a stateless, scalable way to manage user sessions without storing session data on the server.

User Registration

Begin by setting up a MongoDB collection for users. Each user document typically includes fields like username, email, and a hashed password. In your Express.js backend, create a POST /api/register endpoint. Before saving the user, hash the password using bcrypt for security.

User Login

Create a POST /api/login endpoint. When a user provides their credentials, verify the email and compare the submitted password with the hashed password stored in the database using bcrypt’s compare method. If the credentials are valid, generate a JWT using a secret key with the jsonwebtoken library. The payload typically includes the user’s ID or username.

Example:

const token = jwt.sign({ id: user._id }, process.env.JWT_SECRET, { expiresIn: '1h' });

Return this token to the client. The token will be stored in the client’s localStorage or a secure HTTP-only cookie.

Protecting Routes

To secure API endpoints, create Express middleware that checks for the presence of a valid JWT in the Authorization header (Bearer token). In your middleware, verify the token with jwt.verify. If the token is valid, allow the request to continue; otherwise, respond with a 401 Unauthorized error.

Example middleware:

function authenticateToken(req, res, next) {

  const token = req.headers.authorization?.split(' ')[1];

  if (!token) return res.status(401).json({ message: 'Access denied' });

  jwt.verify(token, process.env.JWT_SECRET, (err, user) => {

    if (err) return res.status(403).json({ message: 'Invalid token' });

    req.user = user;

    next();

  });

}

Frontend Integration

In your React app, send the JWT in the Authorization header with protected API requests:

axios.get('/api/protected', { headers: { Authorization: `Bearer ${token}` } });

Use React Router to redirect users based on authentication status, and manage the token in React context or global state.

JWT-based authentication in the MERN stack ensures secure, scalable, and stateless user management—perfect for modern web apps.

Learn MERN Stack Training Course

Read More:

Managing State in React with Context API

Deploying Your MERN App on Vercel

CRUD Operations Using MERN Stack

Building a To-Do App Using MERN Stack

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