public function getAssetContentKeys($asset)
    {
        $assetId = Utilities::getEntityId(
            $asset,
            'WindowsAzure\MediaServices\Models\Asset'
        );

        $propertyList = $this->_getEntityList("Assets('{$assetId}')/ContentKeys");
        $result = [];

        foreach ($propertyList as $properties) {
            $result[] = ContentKey::createFromOptions($properties);
        }

        return $result;
    }