public async Task <IActionResult> ConfirmPhone(string username, string phonenumber, string code)
        {
            var pars = new[] { username, phonenumber, code };

            if (pars.Any(string.IsNullOrWhiteSpace))
            {
                return
                    (Res.PlainUtf8(
                         "One or more of required fields username, phonenumber and code were missing or empty.", 400));
            }

            var user = await _userManager.FindByNameAsync(username);

            var valid = await _userManager.VerifyChangePhoneNumberTokenAsync(user, code, phonenumber);

            if (!valid)
            {
                return(Res.PlainUtf8("Invalid Code", 400));
            }
            user.PhoneNumber          = phonenumber;
            user.PhoneNumberConfirmed = true;
            var res = await _userManager.UpdateAsync(user);

            return(res.Succeeded
                ? Res.PlainUtf8("Success, phone number confirmed.")
                : Res.PlainUtf8(res.PrettyErrors(), 500));
        }