code: func (bto *BootstrapTokenOptions) ApplyTo(cfg *kubeadmapiv1beta2.InitConfiguration) error {
  	if len(bto.TokenStr) > 0 {
  		var err error
  		bto.Token, err = kubeadmapiv1beta2.NewBootstrapTokenString(bto.TokenStr)
  		if err != nil {
  			return err
  		}
  	}
  
  	// Set the token specified by the flags as the first and only token to create in case --config is not specified
  	cfg.BootstrapTokens = []kubeadmapiv1beta2.BootstrapToken{*bto.BootstrapToken}
  	return nil
  }
docs: // ApplyTo applies the values set internally in the BootstrapTokenOptions object to a InitConfiguration object at runtime
  // If --token was specified in the CLI (as a string), it's parsed and validated before it's added to the BootstrapToken object.