Authentication & Authorization

• Topic: “Implementing Authentication with JWT”
• Description: How to implement authentication and authorization using JSON Web Tokens (JWT).

Content:

1. Introduction to JWT

• What is JWT: Explain JSON Web Tokens and their structure.
• Why JWT: Discuss the benefits of using JWT for authentication.

2. Setting Up JWT

• Install Dependencies:

  npm install jsonwebtoken bcryptjs
  

• Configure JWT:

const jwt = require(‘jsonwebtoken’);
const bcrypt = require(‘bcryptjs’);

const secret = 'your_jwt_secret'; // Use an environment variable in real applications
```

3. User Model and Registration

• Define User Schema:

  const userSchema = new mongoose.Schema({ username: { type: String, required: true, unique: true }, password: { type: String, required: true }
  }); userSchema.pre('save', async function(next) { if (this.isModified('password')) { this.password = await bcrypt.hash(this.password, 10); } next();
  }); const User = mongoose.model('User', userSchema);
  

• User Registration Endpoint:

  app.post('/register', async (req, res) => { const user = new User(req.body); try { await user.save(); res.status(201).json(user); } catch (err) { res.status(400).json({ error: err.message }); }
  });
  

4. User Login and Token Generation

• Login Endpoint:

  app.post('/login', async (req, res) => { const { username, password } = req.body; try { const user = await User.findOne({ username }); if (user && await bcrypt.compare(password, user.password)) { const token = jwt.sign({ id: user._id, username: user.username }, secret, { expiresIn: '1h' }); res.json({ token }); } else { res.status(401).send('Invalid credentials'); } } catch (err) { res.status(500).json({ error: err.message }); }
  });
  

5. Protecting Routes with Middleware

• Authentication Middleware:

  const authMiddleware = (req, res, next) => { const token = req.header('Authorization').replace('Bearer ', ''); if (!token) { return res.status(401).send('Access denied'); } try { const decoded = jwt.verify(token, secret); req.user = decoded; next(); } catch (err) { res.status(400).send('Invalid token'); }
  };
  

• Protecting an Endpoint:

  app.get('/profile', authMiddleware, async (req, res) => { try { const user = await User.findById(req.user.id); res.json(user); } catch (err) { res.status(500).json({ error: err.message }); }
  });
  

6. Testing Authentication

• Using Postman: Demonstrate how to register a user, log in to receive a JWT, and use the JWT to access protected routes.
• Example Workflow:
  1. Register a new user at /register.
  2. Log in with the new user at /login to get a token.
  3. Access the protected /profile route using the token in the Authorization header.

This detailed breakdown for weeks 7 to 10 includes explanations and hands-on code examples to provide a comprehensive learning experience.