*     is -1 if signing cert is a lone self-signed certificate.
   */
  private fun verifySignature(
    toVerify: X509Certificate,
    signingCert: X509Certificate,
    minIntermediates: Int,
  ): Boolean {
    if (toVerify.issuerDN != signingCert.subjectDN) {
      return false
    }
    if (signingCert.basicConstraints < minIntermediates) {