Twitch Connect - app ids shared in api
At the moment I have not found any way to get users app id (in my case Riot Account ID) which would allow me to authenticate user using Twitch API and at the same time make sure that user owns this Riot Account. Currently Riot does not support their own way of authentication for third-party developers, therefore Twitch would be great in this case if they shared app ids connected to the Twitch accounts.
The applications that Twitch users authenticate using their Twitch accounts is private information and therefore something we would not share via third-party APIs.
For your specific use case, it may have to be a feature request for Riot. Usually developers link Twitch accounts and game accounts by having the same user authenticate a third-party application they own in both services. Riot would need to provide user authentication to their API to make this possible (as you know).