There are a few requirements to use an existing project as an extension, such as loading the Twitch Extension Helper, and passing a callback to the onAuthorized function.
As well as that there are also guidelines your extension must follow, all of which are listed in the docs, one of the important ones for frontends that use a bundler like Webpack is that it must be set to not use uglification when bundling as the code must be human readable to pass review.