在涉及基于阿里云oss服务的时候，绝大多数情况都是基于表单上传，服务器端生成所需要的信息，这样可以不走本身服务器的流量，灵活并且方便控制。原来基于Java实现的，oss的Java客户端提供了很方便的方法生成policy和signature，golang的客户端貌似没有便捷的方法。以下实现的代码片段仅供参考。

func (s *ossFileService) GetUploadToken(uploadFile model.OssUploadFile) *model.OssUploadToken {
    ossBucket := s.ossBucketRepository.FindById(uploadFile.FileType)

    if ossBucket.Id > 0 {
        fileKey := generateFileKey(uploadFile)

        fileEntity := new(repository.OssFile)

        fileEntity.BucketId = ossBucket.Id
        fileEntity.FileKey = fileKey
        fileEntity.SourceFile = uploadFile.SourceFile
        fileEntity.SourceFileSize = uploadFile.SourceFileSize
        fileEntity.DelStatus = 0

        now := time.Now()

        fileEntity.CreateTime = now
        fileEntity.UpdateTime = now

        result := s.ossFileRepository.Create(*fileEntity)

        bucketType := ossBucket.BucketType
        bucket := ossBucket.Name
        endpoint := ossBucket.Endpoint
        domain := ossBucket.Domain
        accessKeyId := s.ossClient.Config.GetCredentials().GetAccessKeyID()
        secretAccessKey := s.ossClient.Config.CredentialsProvider.GetCredentials().GetAccessKeySecret()
        uploadUrl := fmt.Sprintf("//%s.%s", bucket, endpoint)

        expiration := time.Now().Add(time.Duration(30 * time.Minute)).UTC().Format(time.RFC3339Nano)
        policyStr := fmt.Sprintf(`{"expiration":"%s","conditions":[{"bucket":"%s"},["eq","$key","%s"]]}`, expiration, bucket, fileKey)

        fmt.Println(policyStr)

        policy := base64.StdEncoding.EncodeToString([]byte(policyStr))

        key := []byte(secretAccessKey)
        mac := hmac.New(sha1.New, key)
        mac.Write([]byte(policy))

        signature := base64.StdEncoding.EncodeToString(mac.Sum(nil))

        return &model.OssUploadToken{
            FileId:      result.Id,
            UploadUrl:   uploadUrl,
            AccessKeyId: accessKeyId,
            Policy:      policy,
            Signature:   signature,
            Key:         fileKey,
            Url:         getUrl(bucketType, bucket, endpoint, fileKey, domain)}

    }

    return nil
}