The reason as to why it’s working when you’re pasting it in your browser is because you’re logged in to Twitch on your browser. If you were to open an incognito window it would stop working.
You’re setting up your parameters incorrectly though.
Authorization: OAuth -key- is if you’re using a HTTP header.
You want this URL
https://api.twitch.tv/kraken/user?oauth_token=rojwncsqlhard627ho1yer41eqj1za
I would also suggest changing your oauth_token now too, as you’ve just shared it publicly. (Even though you’ve blurred out your email in your paste, it’s viewable from the URL).