我不确定我错过了什么，但似乎无法使我的CORS策略与.NET Core3.1和Angel8客户端一起工作.

Startup.cs:

        public void ConfigureServices(IServiceCollection services)
        {
            // ...

            // Add CORS policy
            services.AddCors(options =>
            {
                options.AddPolicy("foo",
                builder =>
                {
                    // Not a permanent solution, but just trying to isolate the problem
                    builder.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader();
                });
            });

            services.AddControllers();
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseHttpsRedirection();

            // Use the CORS policy
            app.UseCors("foo");

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }

客户端错误消息:

Access to XMLHttpRequest at 'https://localhost:8082/api/auth/' from origin 'http://localhost:4200' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

UPDATE:

虽然我错误地配置了CORS(下面的答案确实有帮助)，但问题的根源是不相关的.另外，在使用CLI运行API和Angular应用程序时，该应用程序运行完全正常——我只是在将它们都部署到web服务器后才遇到这个问题.

这"actual"个问题最终与SQL连接有关，我只是在将平面文件错误日志(log)添加到API并运行SQL Server跟踪后发现该应用程序根本无法连接到SQL.

我通常认为这只会返回500，并且我会在10秒内意识到这个问题-然而，CORS的错误配置意味着实际上永远不会返回500，因为CORS中间件首先出现了故障.This was immensely frustrating to say the absolute least!美元.然而，我想在这里补充一下，如果其他人发现自己处于这种情况，就像我"追错了兔子"，如果你愿意的话.After fixing the CORS configuration, I realized the actual issue was entirely unrelated to CORS.

TL;DR; - Sometimes "Non-CORS" .NET Server-side Errors Can Be Returned as CORS Errors If CORS policies Aren't Set Correctly

参考资料:

https://docs.microsoft.com/en-us/aspnet/core/security/cors?view=aspnetcore-3.1#cors-with-named-policy-and-middleware

https://medium.com/swlh/cors-headers-with-dot-net-core-3-5c9dfc664785个