You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: invisible_captcha_on_signup.rb
    path of file: ./repos/gitlabhq/app/controllers/concerns
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

module InvisibleCaptchaOnSignup
  extend ActiveSupport::Concern

  included do
    invisible_captcha only: :create, on_sp
    
  def on_timestamp_spam_callback
    return unless Gitlab::CurrentSettings.invisible_captcha_enabled

    invisible_captcha_timestamp_counter.increment
    log_request('Invisible_Captcha_Timestamp_Request')

    redirect_to new_user_session_path, alert: InvisibleCaptcha.timestamp_error_message
  end