startup.cs

public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }
        readonly string MyAllowSpecificOrigins = "_myAllowSpecificOrigins";

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();

            services.AddDbContext<ContextIM>(options => options.UseSqlServer(ContextIM.GetConnectionString()));

            services.AddCors(options =>
            {
                options.AddPolicy(MyAllowSpecificOrigins,
                builder =>
                {
                    builder
                                    .AllowAnyOrigin()
                                    .AllowAnyHeader()
                                    .AllowAnyMethod();
                });
            });

        }
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseCors(MyAllowSpecificOrigins);


            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Site}/{action=Index}/{id?}");
            });
        }
    }