code: def cancel(task_id, secret_key=None, url=None):
    
    if not secret_key:
      secret_key = default_key()
    if not url:
      url = default_url()
  
    url = '%s/cancel' % url
    values = {
      'id': task_id,
    }
    return _send_with_auth(values, secret_key, url)
docs: Cancel scheduled task with `task_id`