code: func checkExpiringCerts(chain []*x509.Certificate) (expiringIntermediates []int) {
  	now := time.Now()
  	for i, cert := range chain {
  		if cert.NotAfter.Sub(now).Hours() < 720 {
  			expiringIntermediates = append(expiringIntermediates, i)
  		}
  	}
  	return
  }
docs: // checkExpiringCerts returns indices of certs that are expiring within 30 days.