@Override
    public String toString() {
        return MoreObjects.toStringHelper(this)
                          .add("certificates", certificates)
                          .add("meterIdPrefix", meterIdPrefix)
                          .toString();
    }
A {@link MeterBinder} that provides metrics for TLS certificates.
The following stats are currently exported per registered {@link MeterIdPrefix}.

<ul>
  <li>"tls.certificate.validity" (gauge) - 1 if TLS certificate is in validity period, 0 if certificate
      is not in validity period</li>
  <li>"tls.certificate.validity.days" (gauge) - Duration in days before TLS certificate expires, which
      becomes -1 if certificate is expired</li>
</ul>
core/src/main/java/com/linecorp/armeria/common/metric/CertificateMetrics.java