Startup config

 public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            ConfigureOAuth(app);
            HttpConfiguration config = new HttpConfiguration();
            WebApiConfig.Register(config);
            var tokenCorsPolicy = new CorsPolicy
            {
                AllowAnyOrigin = true,
                AllowAnyHeader = true,
                AllowAnyMethod = true
            };


            var corsOptions = new CorsOptions
            {
                PolicyProvider = new CorsPolicyProvider
                {
                    PolicyResolver = request => Task.FromResult(request.Path.ToString().StartsWith("/token") ? tokenCorsPolicy : null)
                }
            };

            app.UseCors(corsOptions);
            app.UseWebApi(config);
        }

        public void ConfigureOAuth(IAppBuilder app)
        {
            OAuthAuthorizationServerOptions OAuthServerOptions = new OAuthAuthorizationServerOptions()
            {
                AllowInsecureHttp = true,
                TokenEndpointPath = new PathString("/token"),
                AccessTokenExpireTimeSpan = TimeSpan.FromDays(1),
                Provider = new SimpleAuthorizationServerProvider()
            };

            // Token Generation
            app.UseOAuthAuthorizationServer(OAuthServerOptions);
            app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());

        }
    }