从Angular 前端访问ASP.NET Core 8 Web API时出现CORS错误

我已经阅读了所有的解决方案，到目前为止我都试过了，没有一个有效.

我有一个ASP.NET Core8Web API后端和一个混合的.NET8/ANGLE 15前端.前端应用程序可以向API发出GET个请求，但有POST个请求被CORS阻止.

我已经在接口中try 了以下几种方式:

builder.Services.AddCors(options =>
        {
            options.AddDefaultPolicy(builder => {
                builder.WithOrigins("http://localhost:1859");
                builder.WithMethods("GET", "POST");
                builder.AllowAnyHeader();
            });
        });

和

app.UseHttpsRedirection();
app.UseCors();
app.UseAuthorization();

与.一起

builder.Services.AddCors(options =>
        {
            options.AddDefaultPolicy(builder => {
                builder.AllowAnyOrigin();
                builder.AllowAnyMethod();
                builder.AllowAnyHeader();
            });
        });

The controller method (I've tried with 和 without [EnableCors()]):

[HttpPost] 
public async Task<int> Save(SaveContractRequest req)

Angular 服务方法:

saveContract(req: SaveContractRequest) {
    return this.http.post<number>(this.settingsSvc.apiEndpoint + ReimbursementEndPoints.CONTRACTS_SAVE, req);
}

然而，我总是得到这样的错误:

CORS策略已阻止在‘http://localhost/evms.api/api/Reimbursement/Contracts/Save’从源http://localhost:1859‘访问XMLHttpRequest.请求的资源上不存在"Access-Control-Allow-Origin"标头.

I'm at a loss. I can't get any more permissive than "allow any origin, any header, 和 any method". Why doesn't this work? Why can't I call a controller with a POST method?