public void ConfigureAuth(IAppBuilder app)

{

    app.UseCookieAuthentication(new CookieAuthenticationOptions

    {

        AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,

        LoginPath = new PathString("/Account/Login"),

        Provider = new CookieAuthenticationProvider()

        {

            OnApplyRedirect = ctx =>

            {

                if (!IsApiRequest(ctx.Request))

                {

                    ctx.Response.Redirect(ctx.RedirectUri);

                }

            }

        }

    });

    app.UseExternalSignInCookie(DefaultAuthenticationTypes.ExternalCookie);

}

private static bool IsApiRequest(IOwinRequest request)

{

    string apiPath = VirtualPathUtility.ToAbsolute("~/api/");

    return request.Uri.LocalPath.StartsWith(apiPath);

}