HIPAA-Compliant Microservice Architecture for Patient Data Encryption

Design a secure microservices architecture that ensures end-to-end encryption of patient medical records while maintaining HIPAA compliance. Create a modular system using event-driven design that can handle real-time data transformation, with explicit separation between identification layers and clinical data layers. Include robust authentication mechanisms, implement zero-trust security principles, and provide a detailed threat modeling document explaining potential vulnerabilities and mitigation strategies.