How to enable cross origin requests in ASP.NET MVC 4 on POST using Angular 2

Question

I'm trying to make a POST request with CORS.

I've a class that adds the correct response header on my methods inside my controller

using System;
using System.Web.Mvc;

public class AllowCrossSiteAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        filterContext.RequestContext.HttpContext.Response.AddHeader("Access-Control-Allow-Origin", "http://localhost:4200");
        filterContext.RequestContext.HttpContext.Response.AddHeader("Access-Control-Allow-Headers", "*");
        filterContext.RequestContext.HttpContext.Response.AddHeader("Access-Control-Allow-Credentials", "true");

        base.OnActionExecuting(filterContext);
    }
}

and I use it like this

[AllowCrossSite]
public ActionResult GetReportParameters(string IdRapport)

and I get the expected result

But the problem is when I'm trying to make a POST request with a custom header to pass this specific content type

'Content-Type': 'application/json; charset=utf-8'

I'm actually getting these Response headers

So it's like nothing is done about the header even if I'm correctly going in my attribute class.

Here is my front side in Angular 2 service

const headers = new Headers({ 'Content-Type': 'application/json; charset=utf-8' });
const options = new RequestOptions({ headers: headers , withCredentials: true });

const mock = {
  name: 'TitreRegroupement1',
  visible: false,
  type: 'System.String',
  value: 'Test'
};

// tslint:disable-next-line:max-line-length
const body = JSON.stringify({ idRapport: '00392024-d171-4f39-9c5c-97a51f53fd54', filtre: '', exportFormat: '', parameters: data });

return this.http.post('http://localhost:8080/ReportingViewer/ExportReport', body, options)
  .map((response: Response) => {
      return this.extractSingleData(response, Parameters);
  })
  .catch(this.handleError);
}

By using postman there is no problem to declare, the whole thing travel correctly I can access my parameters from the method inside the controller with no problem.

Answer 1

I found how to make it work. First I apply what proposed me sideshowbarker

if (Request.Headers.AllKeys.Contains("Origin", StringComparer.OridinalIgnoreCase) &&
    Request.HttpMethod == "OPTIONS") {
    Response.Flush();
}

and I was missing something in my Headers, I was doing "*" all the way but finally with these parameters it worked

filterContext.RequestContext.HttpContext.Response.AddHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");

for those who are interested in the final form of my class here it is

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

namespace Via.Client.WebMvc
{
    public class AllowCrossSiteAttribute : System.Web.Mvc.ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {    
            filterContext.RequestContext.HttpContext.Response.AddHeader("Access-Control-Allow-Origin", "http://localhost:4200");
            filterContext.RequestContext.HttpContext.Response.AddHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
            filterContext.RequestContext.HttpContext.Response.AddHeader("Access-Control-Allow-Credentials", "true");

            if (filterContext.HttpContext.Request.HttpMethod == "OPTIONS")
            {
                filterContext.HttpContext.Response.Flush();
            }

            base.OnActionExecuting(filterContext);
        }
    }
}