docs: def validate_cookies(session, class_name):
      """
      Checks whether we have all the required cookies
      to authenticate on class.coursera.org. Also check for and remove
      stale session.
      """
      if not do_we_have_enough_cookies(session.cookies, class_name):
          return False
  
      url = CLASS_URL.format(class_name=class_name) + '/class'
      r = session.head(url, allow_redirects=False)
  
      if r.status_code == 200:
          return True
      else:
          logging.debug('Stale session.')
          try:
              session.cookies.clear('.coursera.org')
          except KeyError:
              pass
          return False