yyyymmdd        = "20060102"
)

type serviceType string

const (
	serviceS3  serviceType = "s3"
	serviceSTS serviceType = "sts"
)

// getCanonicalHeaders generate a list of request headers with their values
func getCanonicalHeaders(signedHeaders http.Header) string {
	var headers []string
	vals := make(http.Header)
	for k, vv := range signedHeaders {
		k = strings.ToLower(k)
		headers = append(headers, k)