code: func (proxy *ProxyClient) currentCluster() (*services.Site, error) {
  	sites, err := proxy.GetSites()
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	if len(sites) == 0 {
  		return nil, trace.NotFound("no clusters registered")
  	}
  	if proxy.siteName == "" {
  		return &sites[0], nil
  	}
  	for _, site := range sites {
  		if site.Name == proxy.siteName {
  			return &site, nil
  		}
  	}
  	return nil, trace.NotFound("cluster %v not found", proxy.siteName)
  }
docs: // currentCluster returns the connection to the API of the current cluster