I recently moved from my IISExpress development server to IIS 8.5. Now I am getting this CORS error. All configuration has been set correctly in the code, ASP.NET Core.

Here is my program.cs and my controller:

using Microsoft.AspNetCore.Authentication.Negotiate;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using System.Diagnostics;
using WebApplication2.App_Contexts;

var builder = WebApplication.CreateBuilder(args);
ILoggingBuilder loggingBuilder = builder.Logging.AddConsole();
loggingBuilder.SetMinimumLevel(LogLevel.Debug);

// Add services to the container.
builder.Services.AddCors(opt =>
{
    opt.AddDefaultPolicy( policy =>
        {
            policy.WithOrigins("http://localhost:3000")
            .AllowAnyHeader()
            .AllowCredentials()
            .AllowAnyMethod();
        });
});

builder.Services.AddControllers();
builder.Services.AddDbContext<DEV_IntranetContext>();
builder.Services.AddDbContext<PreAuthContext>();

// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

builder.Services.AddAuthentication(NegotiateDefaults.AuthenticationScheme)
   .AddNegotiate();

builder.Services.AddAuthorization(options =>
{
    // By default, all incoming requests will be authorized according to the default policy.
    options.FallbackPolicy = options.DefaultPolicy;
});

var app = builder.Build();

app.UseStaticFiles();
//app.UseHttpsRedirection();
app.UseCors("CORS");

app.Use(async (context, next) =>
{
    context.Response.Headers.Add("Access-Control-Allow-Origin", "*");
    context.Response.Headers.Add("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
    context.Response.Headers.Add("Access-Control-Allow-Headers", "Content-Type, Accept, Authorization");

    if (context.Request.Method == "OPTIONS")
    {
        context.Response.StatusCode = (int)HttpStatusCode.OK;
        await context.Response.WriteAsync("OK");
        return;
    }

    await next();
});

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

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

AppDomain.CurrentDomain.SetData("ContentRootPath", builder.Environment.ContentRootPath);
AppDomain.CurrentDomain.SetData("WebRootPath", builder.Environment.WebRootPath);

app.MapControllers();
app.Run();

SitemapController.cs:

using Microsoft.AspNetCore.Cors;
using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using WebApplication2.App_Contexts;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using WebApplication2.App_Linq;

namespace MCA.Controllers
{
    [EnableCors("AllowAllOrigins")]
    [ApiController]
    [Route("[controller]")]
    public class SitemapController : ControllerBase
    {
        private readonly DEV_IntranetContext _db;

        public SitemapController(DEV_IntranetContext db)
        {
            _db = db;
        }

        [EnableCors("AllowAllOrigins")]
        [HttpGet]
        public async Task<string> Get()
        {
            var map = Data.Sitemap(_db);
            var sitemap = JArray.Parse(map);
            string? name = MCA.APIUtilities.GetName(HttpContext);

            if (name is not null)
            {
                var user = await new User(name, _db).Initialize();
                var roles = user.Roles.ToList();

                var data = new
                {
                    sitemap,
                    user = new
                    {
                        user = user.Name,
                        roles = string.Join(",", roles).ToLower()
                    }
                };

                var ret = JsonConvert.SerializeObject(data);
                return ret;
            }
            else
            {
                var data = new
                {
                    sitemap,
                    user = ""
                };

                return JsonConvert.SerializeObject(data);
            }
        }
    }
}

I have gone through every tutorials in page I can find. So far as I can tell the code is set up correctly. The calling app is React, but curl doesn’t succeed either.

Thanks