the configuration is defined in _config.scala.js-template and rendered when calling its route:
Note: Do not use the reverse router to reference the config since it should be overwriteable in your application with the same URL
The js configuration renders and gets delivered with an ETAG to prevent browsers from loading it again if unchanged.
The js-configuration from play-cms can be overwritten/extended in your application. See more about this topic there: Frontend (Browser) Development in play-cms-demo