在ASP.NET Core API中启用CORS

Question

我想在我的ASP.NET核心API中启用CORS。因此，我在项目中添加了Microsoft.AspNetCore.Cors包，并在API中添加了以下代码：

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
  String connectionName = "DefaultConnection";
  services.AddDbContext<CityContext>(options => options.UseSqlServer(Configuration.GetConnectionString(connectionName)));
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
  services.AddCors();
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
   app.UseCors(builder => builder
                        .AllowAnyOrigin()
                        .AllowAnyHeader()
                        .AllowAnyMethod()
                        .AllowCredentials());
   if (env.IsDevelopment())
   {
      app.UseDeveloperExceptionPage();
   }
   else
   {
      app.UseHsts();
   }

   app.UseMvc();
}

但这似乎还不够。对我的API的任何GET请求的标头都仍然相同：

Content-Type application/json; charset=utf-8
Date Sat, 13 Oct 2018 17:20:50 GMT
Server Kestrel
Transfer-Encoding chunked
X-Powered-By ASP.NET
X-SourceFiles ...

但是我希望这里有 Access-Control-Allow-Origin -属性。