func (v *vaultCredentialsProvider) IsExpired() bool {
	v.leaseMu.Lock()
	defer v.leaseMu.Unlock()
	return time.Now().After(v.leaseLastRenew.Add(v.leaseDuration))
}
func (v *vaultCredentialsProvider) IsExpired() bool {
	v.leaseMu.Lock()
	defer v.leaseMu.Unlock()
	return time.Now().After(v.leaseLastRenew.Add(v.leaseDuration))
}
// IsExpired returns if the credentials are no longer valid, and need to be
// retrieved.