Security Considerations Client Security Data Storage: Chats stored locally in IndexedDB (not encrypted) XSS Protection: Sanitize all user input before display CSRF: Use CSRF tokens for state-changing operations Server Security CORS: Configure specific origins in production Authentication: Add API keys or JWT tokens Rate Limiting: Prevent abuse with request throttling Input Validation: Validate all incoming chat data Recommendations for Production // Add CORS configuration app.use(cors({ origin: ['https://yourapp.com'], credentials: true })); // Add authentication middleware app.use('/sync', authenticateToken); // Rate limiting const rateLimit = require('express-rate-limit'); app.use(rateLimit({ windowMs: 15 * 60 * 1000, max: 100 })); Data Privacy Local Storage: Inform users data is stored locally Sync Data: Clarify what data is sent to servers Retention: Implement data deletion policies Compliance: Consider GDPR/CCPA requirements for user data