// 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()