In security systems, authentication verifies identity ("Who are you?"), while authorization determines permissions ("What can you do?"). These complementary mechanisms form the foundation of access control.

Common authentication methods include:

// Basic username/password authentication in Node.js
const authenticateUser = async (username, password) => {
  const user = await User.findOne({ username });
  if (!user) throw new Error('User not found');
  
  const isValid = await bcrypt.compare(password, user.password);
  if (!isValid) throw new Error('Invalid credentials');
  
  return user; // Authentication successful
};

Authorization typically involves:

// Role-based authorization middleware in Express.js
const authorizeAdmin = (req, res, next) => {
  if (req.user.role !== 'admin') {
    return res.status(403).json({ error: 'Forbidden' });
  }
  next();
};

// Usage in route
app.get('/admin-dashboard', authenticateUser, authorizeAdmin, (req, res) => {
  // Admin-only content
});

Here's how JWT combines both concepts:

// JWT authentication and authorization flow
const jwt = require('jsonwebtoken');

// Authentication: Generate token
const token = jwt.sign(
  { userId: user.id, role: user.role }, // Payload
  process.env.JWT_SECRET,
  { expiresIn: '1h' }
);

// Authorization: Verify token and check permissions
const verifyToken = (req, res, next) => {
  const token = req.headers.authorization?.split(' ')[1];
  if (!token) return res.status(401).send('Unauthorized');
  
  try {
    const decoded = jwt.verify(token, process.env.JWT_SECRET);
    req.user = decoded; // Attach user data to request
    next();
  } catch (err) {
    return res.status(403).send('Invalid token');
  }
};

Best practices include:

• Always use HTTPS for authentication
• Implement proper session management
• Follow principle of least privilege in authorization
• Regularly audit permissions

Avoid these mistakes:

// BAD: Hardcoding credentials
if (username === "admin" && password === "password123") {
  // Vulnerable to brute force attacks
}

// BAD: Frontend authorization only
// Client-side checks can be bypassed
if (user.role === 'admin') {
  showAdminPanel(); // MUST verify server-side
}

In security systems, authentication and authorization are two fundamental processes that work together but serve distinct purposes:

• Authentication verifies who you are (identity validation)
• Authorization determines what you can do (permission levels)

Authentication typically involves credentials like:

// Basic authentication example in Node.js
const validateUser = (username, password) => {
  const user = db.users.find(u => u.username === username);
  if (!user) return false;
  return bcrypt.compareSync(password, user.passwordHash);
};

Authorization comes after successful authentication. Common patterns include:

// Role-based authorization middleware
const authorize = (requiredRole) => {
  return (req, res, next) => {
    if (req.user.role !== requiredRole) {
      return res.status(403).send('Forbidden');
    }
    next();
  };
};

Here's how they work together in a web application:

// Express.js route with both authentication and authorization
app.post('/admin/dashboard',
  authenticateUser,  // Authentication middleware
  authorize('admin'), // Authorization middleware
  (req, res) => {
    // Admin dashboard logic
  }
);

• OAuth 2.0: Handles both authentication and authorization
• JWT: Often contains both identity and permission claims
• SAML: Primarily for authentication with authorization extensions

1. Always authenticate before authorizing
2. Implement principle of least privilege
3. Use established libraries instead of custom solutions
4. Regularly audit permission assignments