code: def issuer_cert_urls(self):
          
  
          if self._issuer_cert_urls is None:
              self._issuer_cert_urls = []
              if self.authority_information_access_value:
                  for entry in self.authority_information_access_value:
                      if entry['access_method'].native == 'ca_issuers':
                          location = entry['access_location']
                          if location.name != 'uniform_resource_identifier':
                              continue
                          url = location.native
                          if url.lower()[0:7] == 'http://':
                              self._issuer_cert_urls.append(url)
          return self._issuer_cert_urls
docs: :return:
              A list of unicode strings that are URLs that should contain either
              an individual DER-encoded X.509 certificate, or a DER-encoded CMS
              message containing multiple certificates