req, err := http.NewRequest(http.MethodPost, makeTestTargetURL(endPoint, bucketName, "", nil), reader)
	if err != nil {
		return nil, err
	}

	// Set form content-type.
	req.Header.Set("Content-Type", w.FormDataContentType())
	return req, nil
}

func buildGenericPolicy(t time.Time, accessKey, region, bucketName, objectName string, contentLengthRange bool) []byte {
	// Expire the request five minutes from now.

pkg mime/multipart, method (*Writer) CreateFormFile(string, string) (io.Writer, error)
pkg mime/multipart, method (*Writer) CreatePart(textproto.MIMEHeader) (io.Writer, error)
pkg mime/multipart, method (*Writer) FormDataContentType() string
pkg mime/multipart, method (*Writer) WriteField(string, string) error
pkg mime/multipart, type File interface { Close, Read, ReadAt, Seek }
pkg mime/multipart, type File interface, Close() error