CORS is not allowing WAB to connect to my AGOL org

[MitchellOttesen1]

Trying to pull up Web AppBuilder after a few weeks, nothing different has been changed. I'm not able to connect to my AGOL organization. CORS policy seems to be the culprit. Any ideas?

[MitchellOttesen1 · Accepted solution]

Figured it out in case anyone sees this in the future. In the AGOL Organization settings, there's a place where you can whitelist domains. Once you add a domain to the list, CORS will block all other domains. It is best to leave it empty.

[AndresCastillo]

In case anyone wants to know more details on how these CORS errors work, and how leaving the Allow Origins setting blank let's Mitchell's wab instance access, see Hussein Nasser‌'s very cool video:

https://youtu.be/Ka8vG5miErk

[ahargreaves_FW]

I'm suffering from this issue with a WAB Dev edition app accessing content within a 10.6.1 portal but from 2 different servers. My CORS setting is blank, but I still get the issue.