asp.net mvc - CORS is not working in web api with OWIN authentication

Question

In my application i am using web api with token based authentication with CORS support, but when client request for the token, an error occured due to CORS (Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at (my site name) . This can be fixed by moving the resource to the same domain or enabling CORS.)

I had configured everything required for CORS support ( i think so). here my configuration

Owin start up class

   public class Startup
    {
        public void Configuration(IAppBuilder app)
        {


            var config = new HttpConfiguration
            {
                DependencyResolver = new StructureMapWebApiDependencyResolver(container)

            };


            WebApiConfig.Register(config);  // registering web api configuration
            app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll);  // cors for owin token pipeline
            app.UseWebApi(config);
            ConfigureOAuth(app);


        }

        public void ConfigureOAuth(IAppBuilder app)
        {
            var oAuthAuthorizationServerOptions = new OAuthAuthorizationServerOptions()
            {

                AllowInsecureHttp = true,
                TokenEndpointPath = new PathString("/token"),
                AccessTokenExpireTimeSpan = TimeSpan.FromDays(1),
                Provider = new SimpleAuthorizationServerProvider()
            };
            // Token Generation
            app.UseOAuthAuthorizationServer(oAuthAuthorizationServerOptions);
            app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());

        }
    }

And my webapi configuration

public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            config.EnableCors();  // Corse support for Web api
            config.MapHttpAttributeRoutes(); // attribute based urls

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );

        }
    }

here configuration in web.config

<system.webserver>
 <httpProtocol>
      <customHeaders>
        <!-- Adding the following custom HttpHeader will help prevent CORS from stopping the Request-->
        <add name="Access-Control-Allow-Origin" value="*" />
        <add name="Access-Control-Allow-Methods" value="GET, POST, OPTIONS, PUT, DELETE" />
      </customHeaders>
    </httpProtocol>
</system.webserver>

and my request header from mozilla

Accept  application/json, text/plain, */*
Accept-Encoding gzip, deflate
Accept-Language en-US,en;q=0.5
Content-Length  67
Content-Type    application/x-www-form-urlencoded; charset=UTF-8
Host    talenterp
Origin  http://192.168.1.11:85
Referer http://192.168.1.11:85/
User-Agent  Mozilla/5.0 (Windows NT 6.3; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0

The URLs of Apps are

Server app (which should support CORS)

{http://talenterp}

Token end point :

{http://talenterp/token}

Client app

{http://talentmvc:85}

NB: I already added

context.OwinContext.Response.Headers.Add("Access-Control-Allow-Origin", new[] { "*" });

in GrantResourceOwnerCredentials() method of my AuthorizationServerProvider

Answer 1

Be sure you've got only

app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll);

configured, and not also the old style 'config.EnableCors()' in your Global.asax or WebApiConfig. Furthermore: place the above statement as the first one in your owin Startup class. Yes that really makes a difference, setting it later can also cause cors to not work.

public partial class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll);

        ... etc