• Create a FOLDER called ‘keys’ inside project folder.
• Install some dependencies as following:

Npm install jsonwebtoken –save

• Add the login ROUTER routes/index.js
  
  router.post('/login, function(req, res) {
  // find the user
  User.findOne({
  name: req.body.username
  }, function(err, res) {
  if (err) throw err;
  if (!res) {
  res.json({ success: false, message: Login FAILED.' });
  } else if (res) {
  // check if password matches
  if (res.password != req.body.password) {
  res.json({ success: false, message: Login failed. Wrong password.' });
  } else {
  var token = jwt.sign(res, app.get('superSecret'), {
  expiresInMinutes: 1600
  });
  // return the information including token as JSON
  res.json({
  success: true,
  message: 'Valid token!',
  token: token
  });
  }
  } });
  });

• Use the token in application
  
  jwt = require("express-jwt");
  app.use(function(req, res, NEXT) {
  var token = req.body.token || req.query.token || req.headers['x-access-token'];
  if (token) {
  jwt.verify(token, app.get('superSecret'), function(err, DECODED) {
  if (err) {
  return res.json({ success: false, message: 'Invalid token.' });
  } else {
  req.decoded = decoded;
  next();
  }
  });
  } else {
  return res.status(403).send({
  success: false,
  message: 'No token given.'
  });
  }
  });

Npm install jsonwebtoken –save