Chrome App User Authentication?

[Quin Dennis]

OK, Trying to follow the https://developer.chrome.com/apps/app_identity guide on User Authentication, APP_ID, I got, but this suggests there should be a manifest.json file in .../Chrome/User Data/Default/Extensions/.. with the APP_ID in the title, there's not one, in fact there is no folder with the appropriate files in it at all.  There are ones for other Google Web Store apps, but not the one I've uploaded.