FakeNTLMServer/Program.cs

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

var builder = WebApplication.CreateBuilder(args);


// Add services to the container.

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.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();