How to Authenticate without Webpack.config.js?

In the template's starter kit, there was no stand alone "Webpack.config.js" file and without it, I couldn't find a way to configure "apiURL" variable to integrate the real backend. It'd be more like a StackOverflow question but, is it possible to configure it via React.Scripts or any other way or I should add "Webpack.config.js" file as served like in the repo?