Senior .NET Developer (Windows Service & WPF) - Part-time - Worldwide

Overview

We are seeking an experienced .NET Developer to design and build a lightweight, production-ready Windows service and WPF dashboard application for secure, automated file transfers. The solution will run fully on-premise behind firewalls, with Windows Authentication, role-based access, and an offline-first licensing system.

The ideal candidate has deep expertise in .NET 8 (C#), Windows services, WPF frontends, and secure file transfer protocols (SFTP/FTPS). You should have proven experience delivering polished, reliable desktop/service applications with modern UI and strong security practices.

Responsibilities

Architecture & Development

• Design and implement a Windows service with ASP.NET Core Minimal API (HttpSys, Windows Auth).
• Build a polished WPF dashboard (MahApps.Metro, ModernWpf, or similar) for job management, monitoring, and licensing.
• Implement file scheduling and transfer workflows (move, copy, delete, SFTP/FTPS upload).
• Develop robust two-phase upload process with verification, atomic renames, archiving, and quarantine handling.

Scheduling & Automation

• Configure job scheduling with Quartz.NET.
• Ensure job recovery after service restarts, with retry and backoff strategies.

Security & Access

• Enforce Windows login authentication only (no app passwords).
• Role-based access control (Admins/Operators via Windows/AD groups).
• Store credentials securely using DPAPI (LocalMachine).
• TLS-only transfers (SFTP/FTPS) by default; explicit toggle for plain FTP.

Notifications & Licensing

• Integrate MailKit (SMTP/STARTTLS) and optional Microsoft Graph API for email notifications.
• Implement offline-first yearly licensing (ECDSA-signed JSON licences, machine fingerprinting, grace periods, renewal uploads).

Observability & Deployment

• Logging with Serilog (rolling files + Windows Event Log).
• Export job history to CSV/JSON.
• Package solution into a signed MSI installer (WiX/MSI); ensure clean upgrade paths.
• Provide deployment docs and backup/restore guidance.

Required Skills & Experience

• 5+ years professional experience with .NET (C#), including .NET 6/7/8.
• Proven track record building Windows services and WPF desktop applications with modern UI frameworks.
• Strong knowledge of ASP.NET Core APIs, HttpSys hosting, and Windows Authentication.

Hands-on experience with:

• Quartz.NET (job scheduling)

• SFTP (SSH.NET) and FTPS (FluentFTP) file transfers

• MailKit and Microsoft Graph (SMTP/notifications)

• SQLite + EF Core migrations

• Serilog for logging and monitoring

• WiX/MSI installers (signing, upgrade paths)

• Deep understanding of security best practices: TLS, Windows authentication, RBAC, DPAPI.

• Experience with licensing mechanisms (cryptographic signatures, offline validation) is a strong plus.

Nice-to-Have

• Experience with DevExpress/Telerik WPF UI components.
• Knowledge of Squirrel/MSIX auto-updates.
• Familiarity with offline-first licensing systems and ECDSA key handling.
• Exposure to enterprise IT environments (Windows Server, domain-joined machines, group policies).