func buildGenericPolicy(t time.Time, accessKey, region, bucketName, objectName string, contentLengthRange bool) []byte {
	// Expire the request five minutes from now.
	expirationTime := t.Add(time.Minute * 5)

	credStr := getCredentialString(accessKey, region, t)
	// Create a new post policy.
	policy := newPostPolicyBytesV4(credStr, bucketName, objectName, expirationTime)
	if contentLengthRange {

		"Signature=" + signature,
	}
	auth := strings.Join(parts, ", ")
	req.Header.Set("Authorization", auth)

	return nil
}

// getCredentialString generate a credential string.
func getCredentialString(accessKeyID, location string, t time.Time) string {
	return accessKeyID + SlashSeparator + getScope(t, location)
}