Security fixes: Implement comprehensive security enhancements (#232 #…

[iyanumajekodunmi756]

…235 #237 #241)

• Refactor webhook dispatcher to use signed HMAC payloads to verify authenticity for merchants #232: Refactor webhook dispatcher with enhanced HMAC security

  • Add payload normalization for consistent signature generation
  • Implement replay protection with timestamps and nonces
  • Add timing-safe signature verification
  • Enhance webhookDispatcherService with similar security features

• Implement payload size limits on all incoming REST/GraphQL requests to prevent memory exhaustion attacks #237: Implement payload size limits for REST/GraphQL requests

  • Create PayloadSizeLimitMiddleware with configurable limits
  • Add GraphQL-specific payload complexity analysis
  • Implement early rejection via content-length headers
  • Add security violation logging for monitoring
  • Integrate middleware into main application with environment-based configuration

• Add anomaly detection for sudden spikes in subscription cancellations or payment failures #241: Add anomaly detection for subscription cancellations/payment failures

  • Create AnomalyDetectionService with configurable thresholds
  • Implement baseline calculation and spike detection
  • Add real-time monitoring and alerting system
  • Create REST API endpoints for anomaly statistics and configuration
  • Integrate with subscription service for automatic monitoring

• Harden authentication flows by enforcing strict short-lived JWT token expiration and rotation #235: Harden authentication flows with strict JWT expiration and rotation

  • Implement short-lived access tokens (15 minutes default)
  • Add refresh token rotation with automatic cleanup
  • Create token blacklist for immediate revocation
  • Add timing-safe signature verification
  • Implement token rotation endpoints and middleware
  • Add comprehensive token management and cleanup

Security improvements:

• Enhanced webhook signature verification with normalized payloads
• Memory exhaustion attack prevention via payload limits
• Real-time anomaly detection for business metrics
• Strict JWT token lifecycle management with rotation
• Comprehensive security monitoring and logging
• Configurable security thresholds via environment variables
  closes Refactor webhook dispatcher to use signed HMAC payloads to verify authenticity for merchants #232
  closes Harden authentication flows by enforcing strict short-lived JWT token expiration and rotation #235
  closes Implement payload size limits on all incoming REST/GraphQL requests to prevent memory exhaustion attacks #237
  closes Add anomaly detection for sudden spikes in subscription cancellations or payment failures #241

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