FormsAuthentication.SetAuthCookie throwing NullReferenceException in async action

This issue is not specific to Azure - the method FormsAuthentication.SetAuthCookie will throw a null reference exception in an async action when an await statement is called before FormsAuthentication.SetAuthCookie is called.

The easiest solution is to use the following:

        Response.Cookies.Add(FormsAuthentication.GetAuthCookie("user-1", true));

An alternative would be to specify the ticket creation yourself:

        var ticket = new FormsAuthenticationTicket(
            2,
            "user-1",
            DateTime.Now,
            DateTime.Now.AddDays(2),
            true,
            String.Empty,
            "/");

        var encTicket = FormsAuthentication.Encrypt(ticket);

        Response.Cookies.Add(new HttpCookie(".AUTH", encTicket));