request.authority
请求权限伪头域。因为 HTTP/2 允许请求设置 :authority 或 host，如果存在，则此值是从 req.headers[':authority'] 派生的。否则，它是从 req.headers['host'] 派生的。
¥The request authority pseudo header field. Because HTTP/2 allows requests
to set either :authority or host, this value is derived from
req.headers[':authority'] if present. Otherwise, it is derived from
req.headers['host'].