retrieve the auth_token from nsot

    :param url: str
    :param email: str
    :param secret_key: str
    :return: str

def _get_token(url, email, secret_key):
    '''
    retrieve the auth_token from nsot

    :param url: str
    :param email: str
    :param secret_key: str
    :return: str
    '''
    url = urlparse.urljoin(url, 'authenticate')
    data_dict = {"email": email, "secret_key": secret_key}
    query = salt.utils.http.query(url, data=data_dict, method='POST',
                                  decode=True)
    error = query.get('error')
    if error:
        log.error('Cannot obtain NSoT authentication token due to: %s.', error)
        log.debug('Please verify NSoT URL %s is reachable and email %s is valid', url, email)
        return False
    else:
        log.debug('successfully obtained token from nsot!')
        return query['dict'].get('auth_token')