首先配置Web Api：

1. 在Web API專案下，安裝包

Install-Package Microsoft.AspNet.WebApi.Cors

2. 然後在 WebApiModule 的方法Initialize中，新增下面程式碼：（程式碼最好在ConfigureSwaggerUi的上面）

//設定跨域
            var cors = new EnableCorsAttribute("*", "*", "*");
            cors.SupportsCredentials = true;
            GlobalConfiguration.Configuration.EnableCors(cors);
 

上面配置了Web Api的跨域，然後我們想要在Web MVC中也支援跨域。下面我們給出登入模組支援跨域的例子。

然後配置Web MVC專案，讓登入支援跨域：

1.我們建立一個Attribute類，叫做AcceessOriginalAttribute，如下：

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace MagicQCes.Web.Filters
{
    
 
public class AcceessOriginalAttribute : ActionFilterAttribute, IExceptionFilter
    {public void InternalExuteAccessControle(HttpResponseBase response, HttpRequestBase request)
        {
            var header = response.Headers;
            var requestHeader = request.Headers;
            header.Set(
 
"Access-Control-Allow-Origin", requestHeader["Origin"] ?? "http://" + requestHeader["Host"]);
            header.Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");
            header.Set("Access-Control-Max-Age", "3600");
            header.Set("Access-Control-Allow-Headers", "*");
            header.Set("Access-Control-Allow-Credentials", "true");
        }
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            base.OnActionExecuting(filterContext);
        }

        public override void OnActionExecuted(ActionExecutedContext filterContext)
        {
            InternalExuteAccessControle(filterContext.HttpContext.Response, filterContext.HttpContext.Request);
            base.OnActionExecuted(filterContext);
        }

        public override void OnResultExecuting(ResultExecutingContext filterContext)
        {
            base.OnResultExecuting(filterContext);
        }

        public override void OnResultExecuted(ResultExecutedContext filterContext)
        {
            base.OnResultExecuted(filterContext);
        }

        public void OnException(ExceptionContext filterContext)
        {
            filterContext.Result = new JsonResult()
            {
                Data = new { Succeed = 0, Message = filterContext.Exception.Message },
                JsonRequestBehavior = JsonRequestBehavior.AllowGet
            };
            filterContext.ExceptionHandled = true;
        }
    }
}

2.然後，我們在AccountController中，的Login方法中，新增上面屬性，如下：

        [AcceessOriginal]
        public async Task<JsonResult> Login(string usernameOrEmailAddress, string Password)

這樣，登入也支援跨域了。