I managed to use it !
To help a bit more on my case : I was triggering a function with an onclick button. But as @BarryCarlyon told me it’s a redirection, I simply changed it for a link to this href
https://id.twitch.tv/oauth2/authorize?client_id=my_awesome_client_id&redirect_uri=http://localhost:8080/dashboard&response_type=code&scope=clips:edit
By redirecting the user I saw the Accept/Deny webpage and bringed back the user to my dashboard with a url containing items in query like
http://localhost:8080/dashboard?code=another_code&scope=clips%3Aedit
Now I still have to figure out what do I have to do with this new code (I think I have to pass it to every requests I make to say that this request I allowed by Twitch to be performed and avoid CORS issues, please correct me if I’ve misunderstood something).
Hope it helps