An example of working Windows Authentication between:

• Standalone React.js project, generated by Visual Studio
• ASP.NET Core API (.NET 6)

Pay special attention to: Program.cs (C# Project) Properties\launchSettings.json (C# project) src\setupProxy.js (React project)

The example is set up for Backend (Kestrel) configuration. If you change the project to IIS Express configuration, just change the port in setupProxy.js from 5147 to 32817, as seen in launchSettings.json.