// Returns errAuthentication for all other errors.
func metricsRequestAuthenticate(req *http.Request) (*xjwt.MapClaims, []string, bool, error) {
	token, err := jwtreq.AuthorizationHeaderExtractor.ExtractToken(req)
	if err != nil {
		if err == jwtreq.ErrNoTokenInRequest {
			return nil, nil, false, errNoAuthToken
		}
		return nil, nil, false, err
	}
	claims := xjwt.NewMapClaims()

const DefaultSkewTime = 15 * time.Minute

// Authenticates storage client's requests and validates for skewed time.
func storageServerRequestValidate(r *http.Request) error {
	token, err := jwtreq.AuthorizationHeaderExtractor.ExtractToken(r)
	if err != nil {
		if err == jwtreq.ErrNoTokenInRequest {
			return errNoAuthToken
		}
		return errMalformedAuth
	}

	claims := xjwt.NewStandardClaims()