```javascript
const express = require('express');
const app = express();

// Insert code here to setup user authentication middleware

app.listen(3000, () = {
console.log('Server started on port 3000');
});
```Write a code snippet that demonstrates how to add user authentication middleware to an Express.js server setup. Include any necessary dependencies, middleware configurations, and explain the purpose of each step.

Question

```javascript
const express = require('express');
const app = express();

// Insert code here to setup user authentication middleware

app.listen(3000, () => {
  console.log('Server started on port 3000');
});
```Write a code snippet that demonstrates how to add user authentication middleware to an Express.js server setup. Include any necessary dependencies, middleware configurations, and explain the purpose of each step.

Accepted Answer

To add user authentication middleware to an Express.js server setup, you can use the `passport` library along with its strategies.

1. Install the necessary dependencies:
```shell
npm install express passport passport-local
```

2. Initialize `passport` and `passport-local`:
```javascript
const express = require('express');
const app = express();
const passport = require('passport');
const LocalStrategy = require('passport-local').Strategy;
```

3. Create a user model or import an existing one:
```javascript
const User = require('./models/user'); // Replace './models/user' with the path to your User model
```

4. Set up the passport-local strategy:
```javascript
passport.use(new LocalStrategy(
  // Customize the field names as per your user model
  {
    usernameField: 'email',
    passwordField: 'password'
  },
  (email, password, done) => {
    User.findOne({ email: email }, (err, user) => {
      if (err) { return done(err); }
      if (!user) { return done(null, false); }
      if (!user.verifyPassword(password)) { return done(null, false); }
      return done(null, user);
    });
  }
));
```

5. Configure passport to serialize and deserialize user instances:
```javascript
passport.serializeUser((user, done) => {
  done(null, user.id);
});

passport.deserializeUser((id, done) => {
  User.findById(id, (err, user) => {
    done(err, user);
  });
});
```

6. Set up the user authentication middleware in your Express app:
```javascript
app.use(require('cookie-parser')()); // Use any required middleware
app.use(require('body-parser').urlencoded({ extended: true })); // Use any required middleware
app.use(require('express-session')({ secret: 'secret-key', resave: false, saveUninitialized: false })); // Replace 'secret-key' with your desired secret key

app.use(passport.initialize());
app.use(passport.session());
```

7. Add the authentication route to handle login requests:
```javascript
app.post('/login', passport.authenticate('local', { successRedirect: '/dashboard', failureRedirect: '/login' }));
```
Replace `'/dashboard'` and `'/login'` with your desired success and failure redirect routes.

Now, when a user tries to access any route, you can protect it using the `ensureAuthenticated` middleware:
```javascript
function ensureAuthenticated(req, res, next) {
  if (req.isAuthenticated()) {
    return next();
  }
  res.redirect('/login');
}

app.get('/protected', ensureAuthenticated, (req, res) => {
  // Only authenticated users can access this route
  res.send('Protected Route');
});
```

That's it! You have added user authentication middleware to your Express.js server setup using the `passport` library with `passport-local` strategy.

Dependency Resolver | JavaScript

Adding User Authentication Middleware to an Express.js Server using

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