code: func (s *Sanitizer) KeepAlive(ctx context.Context, lease Lease, expires time.Time) error {
  	if !isKeySafe(lease.Key) {
  		return trace.BadParameter(errorMessage)
  	}
  	return s.backend.KeepAlive(ctx, lease, expires)
  }
docs: // KeepAlive keeps object from expiring, updates lease on the existing object,
  // expires contains the new expiry to set on the lease,
  // some backends may ignore expires based on the implementation
  // in case if the lease managed server side