In order to obtain an OAuth token, you need to supply a client id. For example, like the process detailed outlined in the OAuth Implicit Code Flow. Basically, all a client id does is make it so Twitch can track what app is making what requests and provides no unique access. An OAuth token is a password of sorts, that can grant special permissions to make certain requests. Every OAuth token has a client id associated with it and can be extracted when used, which is why it can be supplied independently of a client id.