//     - http://docs.aws.amazon.com/AmazonS3/latest/dev/auth-request-sig-v2.html
// returns true if matches, false otherwise. if error is not nil then it is always false

func validateV2AuthHeader(r *http.Request) (auth.Credentials, APIErrorCode) {
	var cred auth.Credentials
	v2Auth := r.Header.Get(xhttp.Authorization)
	if v2Auth == "" {
		return cred, ErrAuthHeaderEmpty
	}