func (iamOS *IAMObjectStore) PurgeExpiredSTS(ctx context.Context) error {
	if iamOS.objAPI == nil {
		return errServerNotInitialized
	}

	bootstrapTraceMsg("purging expired STS credentials")

	iamListing, ok := iamOS.cachedIAMListing.Load().(map[string][]string)
	if !ok {
		// There has been no store yet. This should never happen!
		iamLogIf(GlobalContext, errors.New("WARNING: no cached IAM listing found"))
		return nil