.NET版本的OSS的web直传,一直报签名错误（SignatureDoesNotMatch）

这个问题估计要骂骂写java版本demo的人了. 上java代码段:

String postPolicy = client.generatePostPolicy(expiration, policyConds);
byte[] binaryData = postPolicy.getBytes("utf-8");
String encodedPolicy = BinaryUtil.toBase64String(binaryData);
String postSignature = client.calculatePostSignature(postPolicy);

注意看calculatePostSignature方法传入的参数, 感情前面搞了一堆toBase64,这里传的竟然还是原postPolicy字符串. 然而如果你改装成.net了,就千万记得这里要用encodedPolicy去做加密!

分享一个基于阿里云OSS SDK来生成签名的方法代码示例，供参考：

    /// <summary>
    /// 生成浏览器端签名
    /// </summary>
    /// <param name="dir">上传的目标文件夹</param>
    /// <returns>签名信息</returns>
    public OssSignature SignGen(string dir)
    {
        var now = DateTime.Now;
        var ex = now.AddMinutes(30);
        var policyCods = new PolicyConditions();
        policyCods.AddConditionItem("content-length-range", 0L, 1048576000L);
        policyCods.AddConditionItem(MatchMode.StartWith, "key", dir);
        var postPolicy = _ossClient.GeneratePostPolicy(ex, policyCods);
        var binaryData = Encoding.Default.GetBytes(postPolicy);
        var encodedPolicy = Convert.ToBase64String(binaryData);
        var hmac = new HMACSHA1(Encoding.UTF8.GetBytes("你的AccessKeySecret"));
        var hashBytes = hmac.ComputeHash(Encoding.UTF8.GetBytes(encodedPolicy));
        var signature = Convert.ToBase64String(hashBytes);
        DateTime startTime = CurrentTimeZone.ToLocalTime(new DateTime(1970, 1, 1));

        return new OssSignature
        {
            AccessId = XdpOssConfig.AliyunOssConfig.AccessKeyId,
            Policy = encodedPolicy,
            Signature = signature,
            Dir = dir,
            EndPoint = XdpOssConfig.AliyunOssConfig.EndPoint,
            Expire = (long)(ex - startTime).TotalMilliseconds
        };
    }

// 算法参考：https://help.aliyun.com/document_detail/27135.html?spm=5176.8232292.domaindetail.19.IN2iTT
// 核心代码如下，可以参考一下：

var timestamp = (int)(expireDate - new DateTime(1970, 1, 1)).TotalSeconds;
var rand = new Random().Next();
var md5Value = GetMd5(string.Format("/{0}-{1}-{2}-{3}-{4}", key, timestamp, rand, 0, privateKey));
cdnUrl += string.Format("&auth_key={0}-{1}-{2}-{3}", timestamp, rand, 0, md5Value);
return cdnUrl;

我也遇到这个问题，头都大了，官方能不能解决一下

这个最好参考OSS API文档里提供的签名字符串和签名后的值，对一下是签名字符串拼错了，还是SHA1等签名算法用错了。

如果还调试不过，只能发工单找他们的开发来review代码了。