Similar to ._borrow_exported_client, but for CDNs

async def _get_cdn_client(self, cdn_redirect):
        """Similar to ._borrow_exported_client, but for CDNs"""
        # TODO Implement
        raise NotImplementedError
        session = self._exported_sessions.get(cdn_redirect.dc_id)
        if not session:
            dc = await self._get_dc(cdn_redirect.dc_id, cdn=True)
            session = self.session.clone()
            await session.set_dc(dc.id, dc.ip_address, dc.port)
            self._exported_sessions[cdn_redirect.dc_id] = session

        self._log[__name__].info('Creating new CDN client')
        client = TelegramBareClient(
            session, self.api_id, self.api_hash,
            proxy=self._sender.connection.conn.proxy,
            timeout=self._sender.connection.get_timeout()
        )

        # This will make use of the new RSA keys for this specific CDN.
        #
        # We won't be calling GetConfigRequest because it's only called
        # when needed by ._get_dc, and also it's static so it's likely
        # set already. Avoid invoking non-CDN methods by not syncing updates.
        client.connect(_sync_updates=False)
        return client