用户可以在 HTTP 请求中增加 Authorization（授权）的 Head 来包含签名 (Signature)信息，表明这个消息已被授权。 Authorization 字段计算方法如下： "Authorization: OSS " + Access Key Id + ":" + Signature Signature = base64(hmac-sha1(VERB + "\n" + CONTENT-MD5 + "\n" + CONTENT-TYPE + "\n" + DATE + "\n" + CanonicalizedOSSHeaders + CanonicalizedRe