index.js

getConfig()
    .then(
      config => {
      
        fs.readFile(__dirname + '/template.mobileconfig', 'utf-8', (err, template) => {
          const mustacheConfig = {
            CalDAVHostName: config.davserver,
            CalDAVUsername: req.query.username,
            CalDAVPassword: req.query.password,
          };
          const rendered = Mustache.render(template, mustacheConfig);

          res.status(200).json(rendered)
        })
      }
    );
}