🔒 Security Enhancement: HTTP Security Headers Implementation

This PR resolves Issue #54 by implementing comprehensive HTTP security headers to protect against common web vulnerabilities including XSS, clickjacking, and MIME sniffing attacks.

🚀 Changes Summary

✨ New Security Features

• Helmet.js Integration: Added helmet@8.1.0 for robust HTTP header security
• Content Security Policy (CSP): Comprehensive policy to prevent XSS attacks
• HTTP Strict Transport Security (HSTS): Force HTTPS connections
• Clickjacking Protection: X-Frame-Options and Frame-Ancestors configuration
• MIME Type Protection: X-Content-Type-Options to prevent sniffing
• Referrer Policy: Control referrer information disclosure
• Permissions Policy: Browser feature access control

🛠 Configuration & Environment

• Environment Variables: Added security configuration options in .env.example
• Development vs Production: Different configurations for each environment
• Configurable CSP Reporting: Support for CSP violation reporting
• HSTS Configuration: Configurable max-age, subdomain inclusion, and preload

📈 Rate Limiting Enhancements

• General Rate Limiting: 100 requests per 15-minute window
• SSE Connection Limiting: Max 5 SSE connections per minute
• Message Rate Limiting: Max 30 messages per minute
• Critical Operations Limiting: Max 10 critical operations per hour
• User-specific Limits: Per-user rate limiting support

🔧 Technical Improvements

• Endpoint-specific Headers: Custom headers for SSE, health, and API endpoints
• Header Validation: Development-time validation of security headers
• Rate Limit Monitoring: Comprehensive logging and monitoring
• SSE Compatibility: Security headers optimized for Server-Sent Events

📁 Files Modified

Core Implementation

• src/server.ts - Main security implementation with Helmet and custom middleware
• src/config/index.ts - Added security configuration variables

Dependencies

• package.json & package-lock.json - Added helmet and type definitions
• .env.example - Security configuration examples

Documentation

• README.md - Added comprehensive security section with implementation details

🔍 Security Headers Implemented

🧪 Testing

Security Validation

• Headers are automatically validated in development mode
• Missing security headers are logged as warnings
• Rate limiting includes monitoring and alerting

Recommended Validation Tools

• SecurityHeaders.com
• Mozilla Observatory
• Qualys SSL Labs

🚀 Deployment Notes

Environment Configuration

# Production Security Settings
HSTS_MAX_AGE=31536000
CSP_REPORT_ONLY=false
NODE_ENV=production
DISABLE_HSTS=false

# Development Settings  
NODE_ENV=development
CSP_REPORT_ONLY=true
DISABLE_HSTS=true

Rate Limiting

• Configure rate limits based on your traffic patterns
• Monitor rate limit violations in logs
• Adjust critical operation limits for your use case

🔗 Related Issues

• Closes 🟡 MEDIO: Headers de seguridad HTTP faltantes #54 - 🟡 MEDIO: Headers de seguridad HTTP faltantes

📊 Impact Assessment

Security Improvements

• ✅ XSS Protection: CSP prevents script injection
• ✅ Clickjacking Protection: Frame options prevent iframe embedding
• ✅ MIME Sniffing Protection: Content-type enforcement
• ✅ HTTPS Enforcement: HSTS ensures secure connections
• ✅ Information Disclosure: Referrer policy controls data leakage

Performance Impact

• ⚡ Minimal Overhead: Headers add ~200 bytes per response
• 🚦 Rate Limiting: Protects against abuse and DoS
• 📈 Monitoring: Comprehensive logging for security events

Compatibility

• ✅ SSE Support: Headers optimized for Server-Sent Events
• ✅ CORS Compatible: Works with existing CORS configuration
• ✅ Development Friendly: Relaxed policies for development

🔄 Backward Compatibility

• ✅ All existing API endpoints remain functional
• ✅ SSE connections work without modification
• ✅ Environment variables are optional with sensible defaults
• ✅ Development mode maintains debugging capabilities

📝 Additional Notes

This implementation follows OWASP security best practices and provides a solid foundation for web application security. The configuration is flexible enough to adapt to different deployment scenarios while maintaining strong security defaults.

The rate limiting system also provides an additional layer of protection against abuse and ensures fair resource usage across clients.