// Only need the encoding.
	encodedPolicy := base64.StdEncoding.EncodeToString(policy)

	// Presign with V4 signature based on the policy.
	signature := calculateSignatureV2(encodedPolicy, secretKey)

	formData := map[string]string{
		"AWSAccessKeyId":              accessKey,
		"bucket":                      bucketName,
		"key":                         objectName + "/${filename}",