FuelPHP - Auth::create_user?

// Internal server error when using this through jQuery AJAX.
//
// call:
// $.ajax({
//   type: "post",
//   url: "api/signup.json",
//   contentType: "application/x-www-form-urlencoded;charset=UTF-8",
//   data: signupData, // serialized: username=ExampleUser&email=example%40example.tld&password=testpass
//   dataType: "json",
//   success: function(msg) {
//     if('error' in msg) {
//        alert(msg.error);
//     }else {
//        alert(msg.success);
//     }
//  },
//  statusCode: {
//     404: function() {
//        alert('Kontakta webmastern då API:n ej verkar hittas!');
//     }
//  }
// });

public function post_signup() {
        $err = null;
        try {
            $ret = Auth::create_user(
                Input::post('username'),
                Input::post('password'),
                Input::post('email')
            );
        }catch(\SimpleUserUpdateException $e) {
            $err = $e;
        }
            if (null !== $err) {
                return $this->response(array(
                    'error' => $err
                ));
            } else {
                return $this->response(array(
                    'success' => $ret
                ));
            }
    }