If your Twitch extension Local Test suddenly started throwing a CORS error…

Extensions
1

Spent 5+ hours and finally figured this out…. when my local testing stopped working hope this helps!**

Symptom**

  • You’re using Local Test for a Twitch extension.

  • Your Testing Base URI is something like https://localhost:8080/.

  • The Twitch dashboard iframe points at:

    https://localhost:8080/config.html?anchor=panel&...

  • DevTools → Network shows:

    • config.html?... → Status: CORS error

    • Hover tooltip / details:
      Cross-Origin Resource Sharing error: LocalNetworkAccessPermissionDenied

  • Opening https://localhost:8080/config.html directly in a tab works fine.

What’s actually happening

Your CORS and HTTPS can be totally correct and Chrome will still block it.

Recent Chrome versions added a Local Network Access check. A public HTTPS site (like https://dashboard.twitch.tv) isn’t allowed to embed / talk to localhost or your LAN unless the browser grants special local network access permissions.

Twitch’s dashboard iframe doesn’t request that permission, so Chrome refuses the request and mislabels it as a “CORS error” with LocalNetworkAccessPermissionDenied. Your backend never even gets a chance to respond.

2

And thats why my localtest is on a real SSL domain instead of localhost as it’s a more accurate represenatiation of hosted/release