🖥️ POS Updater Client - C# Desktop Application

A lightweight, secure, and autonomous Windows application designed to keep Point of Sale (POS) systems updated seamlessly without disrupting cashier operations.

📋 About the Project

This desktop client is the front-line component of the POS Updater ecosystem. Deployed directly on the cash register machines, it communicates with the POS Updater NestJS API to fetch, verify, and install the latest versions of the main POS software.

It was built with a strong focus on Hardware-Bound Security to ensure that the software can only run on explicitly authorized machines.

✨ Key Features

• 🛡️ Hardware-Bound Encryption (Windows DPAPI): JWT Refresh Tokens and configuration files are encrypted at rest using DataProtectionScope.LocalMachine. If a malicious user copies the application folder to an unauthorized PC, the decryption fails automatically.
• 🔒 TLS 1.2 Enforced Security: All network traffic to the NestJS backend is heavily encrypted in transit.
• 🔄 Autonomous Update Cycle: Runs silently in the background. It authenticates, checks for version discrepancies, downloads the new executable, and registers the download with the central server.
• 🚀 Zero Cashier Friction: Automates the replacement of the .exe file without requiring the cashier to click through installers or input daily credentials.

🏗️ Architecture & Workflow

1. Hardware Fingerprinting: Upon execution, the app reads unique machine identifiers to generate a deviceId.
2. Authentication: Uses the deviceId to log in via the NestJS Server.
3. Secure Storage: The server returns Access and Refresh Tokens, which the C# client encrypts using Windows DPAPI and stores locally as a .dat file.
4. Polling / Checking: The client securely requests the latest version info from the server.
5. Download & Execution: If outdated, it downloads the new PdvFX.exe via an octet-stream, replaces the old binary, and notifies the backend to update the company's Google Sheets dashboard.

🛠️ Tech Stack

• Language: C#
• Framework: .NET (Windows Forms / Console / Worker Service)
• Security: System.Security.Cryptography.ProtectedData (DPAPI), TLS 1.2 Protocol
• Networking: HttpClient for RESTful communication with the Node.js backend

🚀 Installation & Setup

Requirements

• Windows OS (Windows 10 / 11 or Windows Server)
• .NET Runtime installed on the target machine

Configuration

1. Clone the repository and open the solution in Visual Studio.
2. Update the API Base URL in the App.config or appsettings.json file to point to your deployed NestJS Server:

   <appSettings>
     <add key="ApiBaseUrl" value="[https://your-nestjs-api-domain.com/api](https://your-nestjs-api-domain.com/api)" />
   </appSettings>
   Build the solution in Release mode.
   

Deploy the generated .exe and associated .dll files to the target POS machine.

⚠️ Security Notice Do not distribute the .dat token files across different machines. The DPAPI implementation strictly binds the payload to the physical hardware that generated it.