final protected static function _readHeaders()
	{
		if (empty(static::$_request_headers)) {
			$headers = function_exists('getallheaders') ? getallheaders() : [];
			$keys = array_keys($headers);
			array_walk($keys, [__CLASS__, '_cleanHeader']);
			static::$_request_headers = array_combine($keys, array_values($headers));
		}
		return static::$_request_headers;
	}