authenticate in javascript

Authentication in JavaScript can be done through various methods such as token-based authentication, cookies, and sessions. Here we will discuss token-based authentication using JSON Web Tokens (JWT).

Install the jsonwebtoken package from NPM:


npm install jsonwebtoken
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Create an endpoint in the server to generate a token:


index.tsx
const jwt = require('jsonwebtoken');

app.post('/auth', (req, res) => {
  // authenticate the user
  const user = { id: 1, username: 'john' };

  // generate the token
  const token = jwt.sign(user, 'secret_key');

  // send the token to the client
  res.json({ token });
});
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In the client-side, store the token in local storage:


index.tsx
fetch('/auth', {
  method: 'post',
  credentials: 'same-origin',
  body: JSON.stringify({ username, password }),
  headers: { 'Content-Type': 'application/json' }
})
.then(res => res.json())
.then(data => {
  localStorage.setItem('token', data.token);
})
.catch(err => console.error(err));
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Include the token in the headers of the requests to the protected endpoints:


index.tsx
fetch('/api/protected', {
  headers: { 'Authorization': `Bearer ${localStorage.getItem('token')}` }
})
.then(res => res.json())
.then(data => console.log(data))
.catch(err => console.error(err));
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In the server-side, verify the token and authenticate the user:


index.tsx
const jwt = require('jsonwebtoken');

const authenticate = (req, res, next) => {
  // get the token from the headers
  const authHeader = req.headers.authorization;
  const token = authHeader && authHeader.split(' ')[1];

  // verify the token
  jwt.verify(token, 'secret_key', (err, user) => {
    if (err) {
      return res.sendStatus(401);
    }

    // authenticate the user
    req.user = user;
    next();
  });
};

app.get('/api/protected', authenticate, (req, res) => {
  res.json({ message: `Hello ${req.user.username}!` });
});
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This method provides a secure way to authenticate users in JavaScript applications using tokens.

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