'List all server certificates
:param certificate_ids: certificate ids to filter results
:type certificate_ids: ``str``
:return: certificates
:rtype: ``SLBServerCertificate``'

def ex_list_certificates(self, certificate_ids=[]):

    params = {'Action': 'DescribeServerCertificates', 'RegionId': self.region}
    if (certificate_ids and isinstance(certificate_ids, list)):
        params['ServerCertificateId'] = ','.join(certificate_ids)
    resp_body = self.connection.request(self.path, params).object
    cert_elements = findall(resp_body, 'ServerCertificates/ServerCertificate', namespace=self.namespace)
    certificates = [self._to_server_certificate(el) for el in cert_elements]
    return certificates
