code: func (h *Handler) getClusters(w http.ResponseWriter, r *http.Request, p httprouter.Params, c *SessionContext) (interface{}, error) {
  	resource, err := h.cfg.ProxyClient.GetClusterName()
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	response := ui.NewAvailableClusters(resource.GetClusterName(),
  		h.cfg.Proxy.GetSites())
  
  	return response, nil
  }
docs: // getClusters returns a list of clusters
  //
  // GET /v1/webapi/sites
  //
  // Successful response:
  //
  // {"sites": {"name": "localhost", "last_connected": "RFC3339 time", "status": "active"}}
  //