// claim is only considered stable when subject and iss are used together
	// this is to ensure that ParentUser doesn't change and we get to use
	// parentUser as per the requirements for service accounts for OpenID
	// based logins.
	var subFromToken string
	if v, ok := claims[subClaim]; ok {
		subFromToken, _ = v.(string)
	}

	if subFromToken == "" {
		writeSTSErrorResponse(ctx, w, ErrSTSInvalidParameterValue,

//
// Note that returning an error here will cause the Metrics handler to return a
// 500 Internal Server Error.
type MetricsLoaderFn func(context.Context, MetricValues, *metricsCache) error

// JoinLoaders - joins multiple loaders into a single loader. The returned
// loader will call each of the given loaders in order. If any of the loaders
// return an error, the returned loader will return that error.