---name: api-authenticationdescription: Secure API authentication with JWT, OAuth 2.0, API keys. Use for authentication systems, third-party integrations, service-to-service communication, or encountering token management, security headers, auth flow errors.license: MIT---

API Authentication

Implement secure authentication mechanisms for APIs using modern standards and best practices.

Authentication Methods

Method	Use Case	Security Level
JWT	Stateless auth, SPAs	High
OAuth 2.0	Third-party integration	High
API Keys	Service-to-service	Medium
Session	Traditional web apps	High

JWT Implementation (Node.js)

const jwt = require('jsonwebtoken');

const generateTokens = (user) => ({
  accessToken: jwt.sign(
    { userId: user.id, role: user.role },
    process.env.JWT_SECRET,
    { expiresIn: '15m' }
  ),
  refreshToken: jwt.sign(
    { userId: user.id, type: 'refresh' },
    process.env.REFRESH_SECRET,
    { expiresIn: '7d' }
  )
});

const authMiddleware = (req, res, next) => {
  const authHeader = req.headers.authorization;

  // Validate authorization header format
  if (!authHeader || !authHeader.startsWith('Bearer ')) {
    return res.status(401).json({ error: 'Malformed authorization header' });
  }

  const parts = authHeader.split(' ');
  if (parts.length !== 2) {
    return res.status(401).json({ error: 'Malformed authorization header' });
  }

  const token = parts[1];
  if (!token) {
    return res.status(401).json({ error: 'No token provided' });
  }

  try {
    req.user = jwt.verify(token, process.env.JWT_SECRET);
    next();
  } catch (err) {
    res.status(401).json({ error: 'Invalid token' });
  }
};

Security Requirements

• Always use HTTPS
• Store tokens in HttpOnly cookies (not localStorage)
• Hash passwords with bcrypt (cost factor 12+)
• Implement rate limiting on auth endpoints
• Rotate secrets regularly
• Never transmit tokens in URLs

Security Headers

app.use((req, res, next) => {
  res.setHeader('X-Content-Type-Options', 'nosniff');
  res.setHeader('X-Frame-Options', 'DENY');
  res.setHeader('Strict-Transport-Security', 'max-age=31536000');
  next();
});

Additional Implementations

See references/python-flask.md for:

• Flask JWT with role-based access control decorators
• OAuth 2.0 Google integration with Authlib
• API key authentication with secure hashing

Common Mistakes to Avoid

• Storing plain-text passwords
• Using weak JWT secrets
• Ignoring token expiration
• Disabling HTTPS in production
• Logging sensitive tokens