How do I implement authentication middleware in Express.js?

How do I implement authentication middleware in Express.js?

To implement authentication middleware in Express.js, you can create a middleware function that checks for a valid token.

Can you show me a code example of that?

Sure! Here's a simple example:

const jwt = require('jsonwebtoken');

function authenticateToken(req, res, next) {
    const token = req.headers['authorization'];
    if (!token) return res.sendStatus(401);

    jwt.verify(token, process.env.ACCESS_TOKEN_SECRET, (err, user) => {
        if (err) return res.sendStatus(403);
        req.user = user;
        next();
    });
}

This middleware checks for a token in the request headers and verifies it.

What should I do if the token is invalid?

If the token is invalid, you should respond with a 403 status code and a message indicating that access is forbidden.