WCF CORS is set but still getting No 'Access-Control-Allow-Origin' header is present

Question

I am getting this error when attempting to consume a wcf service cross-domain:

XMLHttpRequest cannot load https://MyDomain/MyService.svc/GetData. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'https://CallingDomain' is therefore not allowed access. The response had HTTP status code 500.

I already have set up CORS access in the web.config file like so:

Here is my full web.config file:

Here is my MyService.svc.cs file:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.ServiceModel.Web;
using System.Text;
using System.ServiceModel.Activation;

namespace MyNameSpace
{
    [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Required)]    
    [ServiceContract]
    public class MyService
    {        
        [WebInvoke(Method = "POST",
                    ResponseFormat = WebMessageFormat.Json,
                    BodyStyle = WebMessageBodyStyle.Bare,
                    UriTemplate = "/GetData"
                   )]
        [OperationContract]
        public TestData GetData(string value)
        {
            TestData tsd = TestData.GetTestData(value);

            return tsd;
        } 
    }
}

Here is the ajax I am using to consume the service from a different domain:

function CallService() {
                var params = new Object();
                params.value = "1234";

                var url = "https://ServiceURL/MyService.svc/GetData";

                $.ajax({
                    type: "POST",
                    contentType: "application/json;charset=utf-8",                        
                    url: url,                        
                    data: JSON.stringify(params),                        
                    dataType: "json",
                    success: function (response) {
                        var results = response.d;

                        $.each($(results), function (key, value) {
                            alert(value.Last_Name + " " + value.First_Name);
                        });

                    },
                    error: function (a, b, c) {

                        var warnmsg = "Unable to call service: " + a.responseText;
                        alert(warnmsg);

                    }
                });

            }

I have even also tried setting up CORS through a global.asax file like so:

protected void Application_BeginRequest(object sender, EventArgs e)
    {            
        HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*");
        if (HttpContext.Current.Request.HttpMethod == "OPTIONS")
        {
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "POST, PUT, DELETE");

            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "Content-Type, Accept");
            HttpContext.Current.Response.AddHeader("Access-Control-Max-Age", "1728000");
            HttpContext.Current.Response.End();
        }
    }

Can anyone clue me in to what I am missing here in order to call this service from a different domain?

bdubay · Accepted Answer

We solved this issue by adding an empty method to the MyService.svc.cs file, like so:

[OperationContract]
[WebInvoke(Method = "OPTIONS", UriTemplate = "*")]
void GetOptions() { }

We also added a RequestFormat to the WebInvoke of the GetData POST method like this:

[WebInvoke(Method = "POST",
                    ResponseFormat = WebMessageFormat.Json,
                    BodyStyle = WebMessageBodyStyle.WrappedRequest,
                    RequestFormat = WebMessageFormat.Json
                   )]
        [OperationContract]
        public TestData GetData(string value)
        {
            TestData tsd = TestData.GetTestData(value);  

            return tsd ;
        }

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