A solution would be
- Chrome Extensions opens a popup that goes to Twitch (using
response_typetoken - User accepts (of declines) the link
- User is redrected to your website
- Your website grabs the
#accesstokenand then relays the access token to the extension, or directs the user to copy/paste it into an extension configuration field.
Other solutions might exist but it’s a “how do I build a Chrome extension” thing.