After struggling for a whole evening I finally got this to work. After some debugging I found the problem I was walking into was that my client was sending a so called preflight Options request to check if the application was allowed to send a post request with the origin, methods and headers provided. I didn't want to use Owin or an APIController, so I started digging and came up with the following solution with just an ActionFilterAttribute. Especially the "Access-Control-Allow-Headers" part is very important, as the headers mentioned there do have to match the headers your request will send.

using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace MyNamespace
{
    public class AllowCrossSiteJsonAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            HttpRequest request = HttpContext.Current.Request;
            HttpResponse response = HttpContext.Current.Response;

            // check for preflight request
            if (request.Headers.AllKeys.Contains("Origin") && request.HttpMethod == "OPTIONS")
            {
                response.AppendHeader("Access-Control-Allow-Origin", "*");
                response.AppendHeader("Access-Control-Allow-Credentials", "true");
                response.AppendHeader("Access-Control-Allow-Methods", "GET, PUT, POST, DELETE");
                response.AppendHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, X-RequestDigest, Cache-Control, Content-Type, Accept, Access-Control-Allow-Origin, Session, odata-version");
                response.End();
            }
            else
            {
                HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.NoCache);
                HttpContext.Current.Response.Cache.SetNoStore();

                response.AppendHeader("Access-Control-Allow-Origin", "*");
                response.AppendHeader("Access-Control-Allow-Credentials", "true");
                if (request.HttpMethod == "POST")
                {
                    response.AppendHeader("Access-Control-Allow-Methods", "GET, PUT, POST, DELETE");
                    response.AppendHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, X-RequestDigest, Cache-Control, Content-Type, Accept, Access-Control-Allow-Origin, Session, odata-version");
                }

                base.OnActionExecuting(filterContext);
            }
        }
    }
}

最后，我的MVC动作方法看起来像这样。这里重要的是还要提到Options HttpVerbs，否则preflight请求将失败。

[AcceptVerbs(HttpVerbs.Post | HttpVerbs.Options)]
[AllowCrossSiteJson]
public async Task<ActionResult> Create(MyModel model)
{
    return Json(await DoSomething(model));
}

    public ActionResult ActionName(string ReqParam1, string ReqParam2, string ReqParam3, string ReqParam4)
    {
        this.ControllerContext.HttpContext.Response.Headers.Add("Access-Control-Allow-Origin","*");
         /*
                --Your code goes here --
         */
        return Json(new { ReturnData= "Data to be returned", Success=true }, JsonRequestBehavior.AllowGet);
    }

有时OPTIONS动词也会引起问题

简单: 更新你的网页。配置如下

<system.webServer>
    <httpProtocol>
        <customHeaders>
          <add name="Access-Control-Allow-Origin" value="*" />
          <add name="Access-Control-Allow-Headers" value="Origin, X-Requested-With, Content-Type, Accept" />
        </customHeaders>
    </httpProtocol>
</system.webServer>

用httpGet和httpOptions更新webservice/controller头

// GET api/Master/Sync/?version=12121
        [HttpGet][HttpOptions]
        public dynamic Sync(string version) 
        {

我遇到了一个问题，当请求传入cookie时，浏览器拒绝提供它已经检索到的内容(例如，xhr有它的withCredentials=true)，并且站点有Access-Control-Allow-Origin设置为*。(Chrome中的错误是，“当凭据标志为真时，不能在Access-Control-Allow-Origin中使用通配符。”)

基于@jgauffin的回答，我创建了这个，这基本上是一种绕过特定浏览器安全检查的方法，所以买者自负。

public class AllowCrossSiteJsonAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        // We'd normally just use "*" for the allow-origin header, 
        // but Chrome (and perhaps others) won't allow you to use authentication if
        // the header is set to "*".
        // TODO: Check elsewhere to see if the origin is actually on the list of trusted domains.
        var ctx = filterContext.RequestContext.HttpContext;
        var origin = ctx.Request.Headers["Origin"];
        var allowOrigin = !string.IsNullOrWhiteSpace(origin) ? origin : "*";
        ctx.Response.AddHeader("Access-Control-Allow-Origin", allowOrigin);
        ctx.Response.AddHeader("Access-Control-Allow-Headers", "*");
        ctx.Response.AddHeader("Access-Control-Allow-Credentials", "true");
        base.OnActionExecuting(filterContext);
    }
}

有不同的方式可以通过 Access-Control-Expose-Headers。

正如jgauffin所解释的，我们可以创建一个新属性。 正如LaundroMatt解释的那样，我们可以在网上添加。配置文件。 另一种方法是我们可以在webApiconfig.cs文件中添加如下代码。 配置。EnableCors(new EnableCorsAttribute(""， headers: ""， methods: "*"，exposedHeaders: "TestHeaderToExpose") {SupportsCredentials = true});

或者我们可以在全局中添加以下代码。Asax文件。

protected void Application_BeginRequest()
        {
            if (HttpContext.Current.Request.HttpMethod == "OPTIONS")
            {
                //These headers are handling the "pre-flight" OPTIONS call sent by the browser
                HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST, OPTIONS");
                HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "*");
                HttpContext.Current.Response.AddHeader("Access-Control-Allow-Credentials", "true");
                HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "http://localhost:4200");
                HttpContext.Current.Response.AddHeader("Access-Control-Expose-Headers", "TestHeaderToExpose");
                HttpContext.Current.Response.End();
            }
        }

我写的是期权。请根据您的需要修改。

快乐编码!!

WebAPI 2现在有一个CORS包，可以使用以下方法安装: 安装- package Microsoft.AspNet.WebApi.Cors -pre -project webservice

安装完成后，代码如下所示:http://www.asp.net/web-api/overview/security/enabling-cross-origin-requests-in-web-api