func generateQiniuUpToken(scope, accessKey, secretKey string, sizeLimit int64) string {
mac := qauth.Mac{AccessKey: accessKey, SecretKey: []byte(secretKey)}
policy := qrs.PutPolicy{}
policy.Scope = scope
policy.ReturnBody = `{"key": $(key), "mimeType": $(mimeType), "fsize": $(fsize)}`
policy.FsizeLimit = sizeLimit
return policy.Token(&mac)
}