What is the origin for CORS?

Extensions
2

For an EBS, that your Twitch Extension makes fetch calls to.

Yes, you will need a cors origin header on the server.

In express for example

This allows “everyone”

app.use(cors());

Or you can be specific such as

app.use(cors({
    origin: [
        'https://CLIENTID.ext-twitch.tv',
    ]
}));