protected function store_redis_cache_read($token) {
		if (!$this->redis)
			return null;
		$key = sprintf('%s:%s', $this->token_name, $token);
		$data = $this->redis->get($key);
		if ($data === false)
			# key not fund
			return null;
		$data = @json_decode($data, true);
		if (!$data)
			# cached data is broken
			$data = ['uid' => -2];
		$this->logger->debug(sprintf(
			"Zapmin: session read from cache: '%s' <- '%s'.",
			$token, json_encode($data)));
		return $data;
	}