code: function siteAppsAdmin(req, res, cb) {
    var { themeData } = res.locals;
    const { apps, getInheritTheme, themes } = req.app.locals;
  
    if (!themeData.managingSite) cb();
    else {
      // provide function for apps/themes to add pages
      res.locals.addPages = function(appPages) {
        addPages(req, res, appPages);
      }
  
      let mgSiteApps = themeData.authSites[themeData.managingSite].zsApps;
      if (mgSiteApps) {
        req.app.debug('Site has apps %o', mgSiteApps);
  
        // iterate managingSite apps
        _.forEach(mgSiteApps, function(key) {
          if (apps[key] && apps[key].main) {
            let main = require(`${apps[key].path}/${apps[key].main}`);
  
            // check if middleware for admin is provided
            if (main.admin) {
              main.admin(req, res);
            }
          }
        });
      }
  
      let mgSiteTheme = themeData.authSites[themeData.managingSite].zsTheme;
      if (mgSiteTheme) {
        let themeTree = getInheritTheme(mgSiteTheme);
        // iterate managingSite themetree
        _.forEach(themeTree, function(v, key) {
          if (themes[key] && themes[key].main) {
            let main = require(`${themes[key].path}/${themes[key].main}`);
  
            // check if middleware for admin is provided
            if (main.admin) {
              main.admin(req, res);
            }
          }
        });
      }
  
      cb();
    }
  }
docs: load admin functions for site apps