code: func calculateCAPin(client auth.ClientI) (string, error) {
  	localCA, err := client.GetClusterCACert()
  	if err != nil {
  		return "", trace.Wrap(err)
  	}
  	tlsCA, err := tlsca.ParseCertificatePEM(localCA.TLSCA)
  	if err != nil {
  		return "", trace.Wrap(err)
  	}
  
  	return utils.CalculateSPKI(tlsCA), nil
  }
docs: // calculateCAPin returns the SPKI pin for the local cluster.