指定标头时,jQuery AJAX无法工作(OPTIONS运行前的请求)

AJAX请求工作正常,但是当我通过beforeSend或headers添加标头时,会发出OPTIONS运行前请求并中止GET请求.

  Code: $.ajax({
        type: "GET",
        crossDomain: true,
         beforeSend: function (xhr)
         {
         xhr.setRequestHeader("session", $auth);
         },
        url: $url,
        success: function (data) {
            $('#something').html(data);
        },
        error: function (request, error) {
            $('#something').html("
Error getting values
");
        }
    });

类似的 AJAX请求没有指定标题(当我添加/修改标题时,会进行OPTIONS调用)

Request GET /api/something?filter=1 HTTP/1.1
Referer http://app.xyz.dj/dashboard
Accept  application/json, text/javascript, */*; q=0.01
Accept-Language en-US
Origin  http://app.xyz.dj
Accept-Encoding gzip, deflate
User-Agent  Mozilla/5.0 (Windows NT 6.3; WOW64; Trident/7.0; MASMJS; rv:11.0) like Gecko
Host    162.243.13.172:8080
DNT 1
Connection  Keep-Alive
Cache-Control   no-cache

类似服务器响应标头(用于GET请求)

Response    HTTP/1.1 200 OK
Server  Apache-Coyote/1.1
Access-Control-Allow-Origin *
Access-Control-Allow-Methods    GET, POST, DELETE, PUT, OPTIONS, HEAD
Access-Control-Allow-Headers    Content-Type, Accept, X-Requested-With
Access-Control-Allow-Credentials    true
Content-Type    application/json
Transfer-Encoding   chunked
Date    Thu, 09 Jan 2014 14:43:07 GMT

我做错了什么？