The slack plugin on the marketplace is non-functional. It doesn’t send the identity.basic scope to slack. If added manually to the URL the auth will work successfully.
Will this be fixed? There is a related topic from Dec 21 with the same issue here with no resolution. This is currently a blocker to me using Auth0 for our product.
I did some digging on our backend and assuming I am looking at the correct connection I see that the identity.basic scope is indeed missing from the user_scope value of authParams on your connection. You should be able to see this if you get the connection via the Management API. While I don’t have an explanation as to why this is missing I recommend 2 things:
Delete and recreate the connection to see if the correct scopes come through.
You could use the Management API to update the connection, adding the identity.basic scope.