func isRequestPresignedSignatureV2(r *http.Request) bool {
	_, ok := r.Form[xhttp.AmzAccessKeyID]
	return ok
}

// Verify if request has AWS Post policy Signature Version '4'.
func isRequestPostPolicySignatureV4(r *http.Request) bool {
	mediaType, _, err := mime.ParseMediaType(r.Header.Get(xhttp.ContentType))
	if err != nil {
		return false
	}
	return mediaType == "multipart/form-data" && r.Method == http.MethodPost
}