FakeNTLMServer/Program.cs

using Microsoft.AspNetCore.Authentication.Negotiate;
using Microsoft.OpenApi.Models;
using NLog;
using NLog.Web;

var logger = LogManager.Setup().LoadConfigurationFromAppSettings().GetCurrentClassLogger();
logger.Info("Logging initialized!");

try
{
    var builder = WebApplication.CreateBuilder(args);

    if (!builder.Environment.IsDevelopment())
    {
        builder.Logging.ClearProviders();
        builder.Host.UseNLog();
    }

    builder.Services.AddControllers();
    builder.Services.AddAuthentication(NegotiateDefaults.AuthenticationScheme)
        .AddNegotiate();
    builder.Services.AddAuthorization();
    // Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
    builder.Services.AddEndpointsApiExplorer();
    builder.Services.AddSwaggerGen(options =>
    {
        options.SwaggerDoc("v1", new OpenApiInfo
        {
            Title = "FakeNTLMServer",
            Version = "v1",
            Description = "NTLM/Negotiate authentication test server"
        });

        options.AddSecurityDefinition("Negotiate", new OpenApiSecurityScheme
        {
            Type = SecuritySchemeType.Http,
            Scheme = "Negotiate",
            Description = "Windows Authentication (NTLM/Kerberos). Credentials are sent automatically by the browser."
        });

        options.AddSecurityRequirement(new OpenApiSecurityRequirement
    {
        {
            new OpenApiSecurityScheme
            {
                Reference = new OpenApiReference
                {
                    Type = ReferenceType.SecurityScheme,
                    Id = "Negotiate"
                }
            },
            Array.Empty<string>()
        }
    });

        var xmlFile = $"{System.Reflection.Assembly.GetExecutingAssembly().GetName().Name}.xml";
        var xmlPath = Path.Combine(AppContext.BaseDirectory, xmlFile);
        if (File.Exists(xmlPath))
            options.IncludeXmlComments(xmlPath);
    });

    var app = builder.Build();

    // Configure the HTTP request pipeline.
    if (app.Environment.IsDevelopment() || app.Configuration.GetValue<bool>("EnableSwagger"))
    {
        app.UseSwagger();
        app.UseSwaggerUI(options =>
        {
            // Enable sending credentials (NTLM tokens) with Swagger UI requests
            options.ConfigObject.AdditionalItems["withCredentials"] = true;
        });
    }

    app.UseHttpsRedirection();

    app.UseAuthentication();
    app.UseAuthorization();

    app.MapControllers();

    app.Run();
}
catch (Exception ex)
{
    logger.Error(ex, "Stopped program because of exception");
    throw;
}