code: func readCA(params RegisterParams) (*x509.Certificate, error) {
  	certBytes, err := utils.ReadPath(params.CAPath)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	cert, err := tlsca.ParseCertificatePEM(certBytes)
  	if err != nil {
  		return nil, trace.Wrap(err, "failed to parse certificate at %v", params.CAPath)
  	}
  	return cert, nil
  }
docs: // readCA will read in CA that will be used to validate the certificate that
  // the Auth Server presents.