Enhance Existing C# Application

I already have a working C# application and I now need a seasoned developer to round it out with three key pieces of functionality:

• Implement secure, stateless user authentication using JWT (JSON Web Tokens).
• Wire the app to a SQL database for persistent storage and retrieval, keeping the current schema intact wherever possible.
• Expose or refine REST-style APIs so the updated features are fully accessible to external services.

The codebase is clean and well-documented; you’ll receive the latest repository, a quick architectural overview, and sample data scripts for the SQL instance. I expect production-ready code, thorough unit tests, and brief setup notes so I can pull, build, and run everything without surprises.

If you have deep C#/.NET expertise and can move quickly while following best practices for security and performance, let’s get this shipped.