I simply point to your instruction for setting up irc http://help.twitch.tv/customer/portal/articles/1302780-twitch-irc
Then user is supposed to keep that oauth:password and enter it in game settings.
I see the benefit of having just one token for all scopes but it requires different approach which I am trying to figure.
You said curl can handle authentication. Can you outline the process?
Should I begin as described in Implicit Grant Flow or elsewhere?
If I send request to api.twitch.tv/kraken/oauth2/authorize what is the response - html page?