Use the given username for saying message

[BarryCarlyon]

@Sylvanus

So I see I have to create a separate twitch account, add it as a moderator on the channel in question, generate its access token and then use it in the TMI?

Yes

@Sylvanus

But it is against intuitive in this not to be able to also use it in the subscription has PUB / SUB, where there it is necessary on the other hand the identity and therefore the access_token of the owner of the chain.

The bot uses the a token that represents the bot, that has chat read/write

And to read from pubsub, you use a token that represents you, and has the subscribe scopes (or whatever you need for whichever topics)