If you’re getting a “Client ID and OAuth token do not match” error, it’s because you’re not using an OAuth token generated by your app.
You need to register an app on the TwitchDev portal, that’ll get you a Client ID. Then if you’re making requests server-side you should use the Client Credentials flow to generate an App token.
If you generate tokens using any other site, or anything other than your own client id, you’ll get a mismatch error.
If you want to use User B’s OAuth token, then it’s exactly the same except you’ll send User B through your apps OAuth flow, with Implicit or Auth Code depending on situation, to get an OAuth token from that user. Again, it has to be your apps OAuth flow, and your apps Client ID.