How to Enable Cross Origin Requests in ASP.NET MVC

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

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);
        }
    }
}

Setting Access-Control-Allow-Origin in ASP.Net MVC - simplest possible method

For plain ASP.NET MVC Controllers

Create a new attribute

public class AllowCrossSiteJsonAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        filterContext.RequestContext.HttpContext.Response.AddHeader("Access-Control-Allow-Origin", "*");
        base.OnActionExecuting(filterContext);
    }
}

Tag your action:

[AllowCrossSiteJson]
public ActionResult YourMethod()
{
    return Json("Works better?");
}

For ASP.NET Web API

using System;
using System.Web.Http.Filters;

public class AllowCrossSiteJsonAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
    {
        if (actionExecutedContext.Response != null)
            actionExecutedContext.Response.Headers.Add("Access-Control-Allow-Origin", "*");

        base.OnActionExecuted(actionExecutedContext);
    }
}

Tag a whole API controller:

[AllowCrossSiteJson]
public class ValuesController : ApiController
{

Or individual API calls:

[AllowCrossSiteJson]
public IEnumerable<PartViewModel> Get()
{
    ...
}

For Internet Explorer <= v9

IE <= 9 doesn't support CORS. I've written a javascript that will automatically route those requests through a proxy. It's all 100% transparent (you just have to include my proxy and the script).

Download it using nuget corsproxy and follow the included instructions.

Blog post | Source code

How to enable cross origin requests in ASP.NET MVC?

public static void Register(HttpConfiguration config)
{
    // New code
    config.EnableCors();
}

[EnableCors(origins: "http://systematixindia.com", headers: "*", methods: "*")]
public class TestController : ApiController
{
   // Controller..
}

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