Senior .NET Middleware Developer - Healthcare Interoperability (FHIR / ePA)

Senior .NET Middleware Developer Healthcare Interoperability (FHIR / ePA)
Position: Senior .NET Middleware Developer / Integration Engineer

Domain: US Healthcare / Medicaid / Healthcare Interoperability
Technology: .NET Core / ASP.NET Core / C# / REST APIs / HL7 FHIR
Location: Remote

We are seeking an experienced Senior .NET Middleware Developer to design, develop, integrate, and support middleware services for a large-scale healthcare interoperability program supporting multiple US Medicaid state implementations.
The middleware platform will facilitate secure communication, orchestration, data transformation, and transaction processing between healthcare payer systems, utilization management applications, FHIR-based interoperability platforms, and external healthcare technology partners.
The candidate must possess strong technical expertise in .NET development, API integrations, healthcare data exchange, and distributed application architecture.
Experience implementing healthcare interoperability solutions involving CMS-0057, HL7 FHIR, and Electronic Prior Authorization is highly desirable.
2. Key Responsibilities
A. Middleware Development & Integration
* Design and develop scalable middleware applications using C#, .NET 8+, and ASP.NET Core.
* Develop RESTful APIs and integration services connecting multiple healthcare applications.
* Build orchestration services coordinating transactions across payer systems, UM platforms, and interoperability APIs.
* Implement synchronous and asynchronous communication mechanisms.
* Develop configurable transformation services supporting JSON, XML, CSV, and flat-file formats.
* Build file-based integration services supporting SFTP transfers, file validation, acknowledgments, and exception handling.
* Implement transaction tracking, retry mechanisms, error handling, and reconciliation processes.
* Develop reusable integration components supporting multiple Medicaid state implementations.
B. Healthcare Interoperability & ePA
Support middleware integration requirements associated with:
Coverage Requirements Discovery (CRD)
* Integrate CRD services with applicable payer systems and supporting applications.
* Facilitate retrieval and exchange of coverage requirements, prior authorization requirements, and relevant payer information.
* Support transaction orchestration between CRD APIs and downstream systems.
Documentation Templates and Rules (DTR)
* Support integration with DTR workflows where middleware involvement is required.
* Facilitate exchange of supporting documentation and structured clinical information.
* Implement appropriate data transformation and routing mechanisms.
Prior Authorization Support (PAS)
* Develop integration components between FHIR-based PAS transactions and legacy UM platforms.
* Support conversion of structured API payloads into downstream application-specific formats where required.
* Implement inbound and outbound file-processing workflows.
* Support authorization request submission, status tracking, response processing, and error management.
State-Specific Integration
* Support different integration patterns across Medicaid states.
* Implement configurable routing and transformation rules.
* Integrate existing Gainwell applications and state-specific UM solutions.
* Support hybrid interoperability architectures involving both FHIR APIs and legacy flat-file interfaces.
The exact middleware responsibilities for CRD, DTR, and PAS will depend on each state's approved solution architecture.
C. Application & System Integration
Develop and maintain integrations involving:
* Medicaid enterprise applications
* State-specific utilization management systems
* Onyx interoperability APIs
* Abacus healthcare data platform
* Prior Legacy applications
* External vendor systems
* Secure file-transfer platforms
* Provider-facing healthcare applications, where applicable




Responsibilities include interface development, connectivity validation, payload transformation, transaction orchestration, and integration troubleshooting.




D. API Security & Compliance




* Implement OAuth 2.0 and JWT-based authentication and authorization.
* Support SMART on FHIR integration patterns where applicable.
* Implement secure API communication using TLS.
* Ensure appropriate protection of PHI and sensitive healthcare information.
* Apply HIPAA-aligned security practices.
* Implement structured logging, audit trails, and transaction monitoring.
* Support API gateway integration and security controls.




E. Testing & Production Readiness
* Develop unit and integration tests for middleware components.
* Support system integration testing (SIT), pre-UAT, and UAT.
* Validate end-to-end transaction flows across multiple applications.
* Support performance, load, and scalability testing.
* Troubleshoot integration failures across API and file-based interfaces.
* Support deployment, release management, and production stabilization.
* Collaborate with QA teams to establish automated regression testing.
3. Required Technical Skills
Technology / Skill Requirement
C# Expert
.NET 8+ / ASP.NET Core Expert
REST API development Expert
Microservices architecture Strong
JSON / XML / CSV processing Strong
SFTP and flat-file integrations Strong
API orchestration Strong
SQL Server / relational databases Strong
OAuth 2.0 / JWT Strong
Git / Azure DevOps Strong
CI/CD pipelines Strong
Docker / containerization Preferred
HL7 FHIR R4 Preferred
Healthcare EDI / X12 Preferred
Azure / AWS Preferred
Distributed messaging / queues Preferred
4. Healthcare Domain Knowledge

Highly desirable:




* US Medicaid and Medicaid Management Information Systems (MMIS)




* Healthcare payer operations




* Prior authorization workflows




* Utilization management systems




* CMS Interoperability and Prior Authorization Final Rule (CMS-0057-F)




* HL7 FHIR R4




* Da Vinci CRD, DTR, and PAS implementation guides




* Provider-to-payer integration workflows




* Healthcare API and legacy application interoperability




Experience working with multiple healthcare vendors and integrating legacy payer systems with modern FHIR APIs will be a significant advantage.




5. Architecture & Engineering Expectations




The candidate should be capable of




1. Understanding complex healthcare integration architecture.




2. Translating interface specifications into technical designs.




3. Developing reusable middleware components.




4. Implementing configurable state-specific integration logic.




5. Designing reliable asynchronous processing mechanisms.




6. Building robust transaction monitoring and error-handling capabilities.




7. Supporting high-volume healthcare transaction processing.




8. Working across multiple technical teams and external vendors.




6. Key Deliverables




The developer will be accountable for producing:




* Middleware technical design documents




* API interface specifications




* Integration sequence diagrams




* Source code and reusable components




* Data mapping and transformation specifications




* File-processing and transaction-handling services




* Unit and integration test results




* Deployment configurations




* Technical troubleshooting documentation




* Production support and operational runbooks




7. Collaboration & Stakeholder Engagement




The developer will work closely with:




* Middleware technical architects




* Onyx API development teams




* Abacus integration teams




* State-specific UM application teams




* Business analysts




* QA and integration testing teams




* Infrastructure and security teams




* Program and project management teams




The candidate should be comfortable working in a multi-vendor environment with complex technical dependencies and delivery milestones.




8. Preferred Candidate Profile




An ideal candidate will have:




* 7+ years of professional software development experience.




* 5+ years of hands-on .NET / C# development.




* 3+ years of API and enterprise integration development.




* Experience integrating legacy applications with modern REST APIs.




* Strong understanding of distributed systems and integration patterns.




* Prior experience in US healthcare payer or Medicaid environments.




* Ability to independently own middleware components from design through deployment.




9. Interview Evaluation Criteria




Candidates should demonstrate their ability to:




Design an end-to-end API-to-flat-file integration.




Explain asynchronous processing, retries, and transaction recovery.




Develop secure RESTful APIs using .NET.




Handle complex JSON payload transformations.




Implement SFTP-based file exchange.




Troubleshoot cross-application integration failures.




Design middleware components that can be reused across multiple states.




Explain how FHIR-based prior authorization transactions can integrate with legacy UM systems.




Priority: Strong .NET integration engineering expertise is mandatory. Healthcare/FHIR expertise is highly desirable, but candidates with excellent enterprise integration experience and the ability to learn healthcare workflows should also be considered.