ajax - CORS enabled but response for preflight has invalid HTTP status code 404 when POSTing JSON

Question

I've searched thoroughly but cannot find a solution to this issue in my particular circumstance.

Cross-domain service calls using Fiddler (POST) execute correctly and the data is received. However, through the browser (Chrome) I am getting the message 'preflight has invalid HTTP status code 404'

I have a Web API application and have installed CORS and ensured the following is present in the web.config file:

<system.webServer>
    <handlers>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <remove name="OPTIONSVerbHandler" />
      <remove name="TRACEVerbHandler" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
    </handlers>
    <httpProtocol>
      <customHeaders>
        <add name="Access-Control-Allow-Origin" value="*" />
        <add name="Access-Control-Allow-Headers" value="Content-Type" />
        <add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS" />
      </customHeaders>
    </httpProtocol>
</system.webServer>

Here is the Ajax call:

var secretKey = 'difusod7899sdfiertwe08wepifdfsodifyosey',
    url = 'http://api.intrinsic.co.uk/api/v1/PTS/ActiveDrivers?api_key=098werolllfWnCbPGAuIXVOJidDHRfYcgxImMlxTXopuekXrSOqOWzEAIdeNTWGPQPpyHxgVGsFysGFKPzq';

  jQuery.ajax ({
      url: url,
      type: "POST",
      data: JSON.stringify({ secretKey: secretKey}),
      dataType: "json",
      contentType: "application/json; charset=utf-8",
      success: function(data){
          var content = "<table class="container"><thead><tr><th>Driver Number</th><th>Timestamp</th><th>VRN</th><th>Latitude</th><th>Longitude</th><th>Track Link</th></tr></thead><tbody>";
          $.each(data.ActiveDrivers.DriverLocationStatus, function (index, element) {
              content += "<tr><td>" + element.DriverNumber + "</td>";
              content += "<td>" + dateFormat(element.Timestamp, "d/m/yy") + " " + dateFormat(element.Timestamp, "h:MM TT") + "</td>";
              content += "<td>" + element.VRN + "</td>";
              content += "<td>" + element.CurrentLatitude + "</td>";
              content += "<td>" + element.CurrentLongitude + "</td>";
              content += "<td><a href="https://www.google.co.uk/maps/place//@" + element.CurrentLatitude + "," + element.CurrentLongitude + ",15z/" target='_blank'>Track &raquo;</a></td></tr>";
          });
          content += "</tbody></table>";
          $( "#result" ).html( content );
      }
  });

Obviously, works on the same domain perfectly and, as mentioned, it works using Fiddler.

I'm certain it is the browser's preflight OPTIONS check that is failing for content-type of 'application/json' but I'm not sure how to fix it.

Is there something missing in the web.config file that I should add?

I have tried removing 'content-type' with no affect.

I had hoped this article would solve the issue (it seemed promising) but the same error is encountered:

XMLHttpRequest cannot load [URL]. Response for preflight has invalid HTTP status code 404

Answer 1

Thanks but getting 405 error,after the above config changes.

Finally it works after adding below code in web api Global.asax file

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("Cache-Control", "no-cache");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST");
            HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "Content-Type, Accept");
            HttpContext.Current.Response.AddHeader("Access-Control-Max-Age", "1728000");
            HttpContext.Current.Response.End();
        }
    }