用过php签名的，大神帮忙看看

//以下代码 用php签名
    $headerSign=base64_encode(hash_hmac('sha1','POST\nODBGOERFMDMzQTczRUY3NUE3NzA5QzdFNUYzMDQxNEM=\ntext/html\nThu,Feb 25 2017 10:19:50 GMT\nx-oss-magic:abracadabra\nx-oss-meta-author:foo@bar.com\n/oss-example/nelson','我的密钥',true));

//前端使用ajax
ajax.open('POST','http://ketu.oss-cn-shenzhen.aliyuncs.com/uploading/test.mp4?uploadId=0004B999EF5A239BB9138C6227D69F9',true);
ajax.setRequestHeader('Authorization','OSS 我的AccessID:'+headerSign);//设置头带上签名信息
ajax.send();

一直都是OSS authentication requires a valid Date  403