code: func (a *AuthCommand) RotateCertAuthority(client auth.ClientI) error {
  	req := auth.RotateRequest{
  		Type:        services.CertAuthType(a.rotateType),
  		GracePeriod: &a.rotateGracePeriod,
  		TargetPhase: a.rotateTargetPhase,
  	}
  	if a.rotateManualMode {
  		req.Mode = services.RotationModeManual
  	} else {
  		req.Mode = services.RotationModeAuto
  	}
  	if err := client.RotateCertAuthority(req); err != nil {
  		return err
  	}
  	if a.rotateTargetPhase != "" {
  		fmt.Printf("Updated rotation phase to %q. To check status use 'tctl status'\n", a.rotateTargetPhase)
  	} else {
  		fmt.Printf("Initiated certificate authority rotation. To check status use 'tctl status'\n")
  	}
  
  	return nil
  }
docs: // RotateCertAuthority starts or restarts certificate authority rotation process