code: func cacheUnmanagedCertificatePEMFile(certFile, keyFile string) error {
  	cert, err := makeCertificateFromDisk(certFile, keyFile)
  	if err != nil {
  		return err
  	}
  	cacheCertificate(cert)
  	return nil
  }
docs: // cacheUnmanagedCertificatePEMFile loads a certificate for host using certFile
  // and keyFile, which must be in PEM format. It stores the certificate in
  // memory. The Managed and OnDemand flags of the certificate will be set to
  // false.
  //
  // This function is safe for concurrent use.