code: def set_cdn_metadata(self, container, metadata):
          
          allowed = ("x-log-retention", "x-cdn-enabled", "x-ttl")
          hdrs = {}
          bad = []
          for mkey, mval in six.iteritems(metadata):
              if mkey.lower() not in allowed:
                  bad.append(mkey)
                  continue
              hdrs[mkey] = str(mval)
          if bad:
              raise exc.InvalidCDNMetadata("The only CDN metadata you can "
                      "update are: X-Log-Retention, X-CDN-enabled, and X-TTL. "
                      "Received the following illegal item(s): %s" %
                      ", ".join(bad))
          uri = "%s/%s" % (self.uri_base, utils.get_name(container))
          resp, resp_body = self.api.cdn_request(uri, "POST", headers=hdrs)
          return resp
docs: Accepts a dictionary of metadata key/value pairs and updates
          the specified container metadata with them.
  
          NOTE: arbitrary metadata headers are not allowed. The only metadata
          you can update are: X-Log-Retention, X-CDN-enabled, and X-TTL.