How can I fix my cors error in ASP.NET Core 8 app?

Question

For several days now, I've been trying to solve a CORS problem I'm having, however I already did a lot of attempts in the Program.cs file to try to solve this but I can't figure this out.

Basically the CORS error only happens on POST methods.

I have this code in Program.cs:

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddHttpClient();

builder.Services.AddCors(builder =>
{
    builder.AddPolicy("AllowAll", options =>
    {
        options.AllowAnyOrigin()
            .AllowAnyMethod()
            .AllowAnyHeader();
    });
});

var app = builder.Build();

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

app.UseHttpsRedirection();
app.UseRouting();

app.UseCors("AllowAll");

app.UseAuthorization();

app.MapControllers();

app.Run();

In the browser console I see this:

Access to XMLHttpRequest at 'https://localhost:7278/api/Topaz/SetTabletState' from origin 'https://example.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Can anyone help me figure this out?

I already tried to put the domain on the origins but still does not work.

I already tried to define the CORS policy in the controller but still does not work.

Answer 1

After systematic debugging, I conducted a test using XMLHttpRequest as an alternative to AJAX. Interestingly, I discovered that setting the "datatype" parameter to "jsonp" on AJAX effectively resolves the issue at hand. Notably, when employing XMLHttpRequest for making requests, no Cross-Origin Resource Sharing (CORS) errors were encountered.

Also, using XMLHttpRequest does not give me any CORS error and works as expected!