Problem using GitHub OAuth instead of Netlify identity

I have followed instructions in https://www.netlify.com/docs/authentication-providers/ including the setup in my Netlify site.

Yet, I’m still getting this error message:
image

instead of the expected dialog in the demo https://auth-demo.netlify.com/vanilla-js-example

What am I doing wrong?

Hi @pdesmarets,

I noticed you posted this in the Netlify CMS category, is this an issue with the Netlify CMS and the github backend or are you trying to do something else? The example you linked was not for the CMS. Can you also share a link to the site you are testing on? Thanks.