code: def login_checking_email(pending_id, ticket, response, detail_url='https://pswdless.appspot.com/rest/detail'):
      
      return LoginCheckingEmail(pending_id, ticket, response, USER_COOKIE_NAME, detail_url)
docs: Log user in using Passwordless service
      :param pending_id: PendingExternalToMainUser's id
      :param ticket: ticket returned from Passwordless
      :param response: Response object from webapp2
      :param detail_url: url to check ticket and user data
      :return: a Command that log user in when executed