One random idea, not sure how practical - Do a screenshot analysis/pattern matching on all customer login pages. If verbiage or screenshot matches are close enough, it get's flagged for human review. This would only work on the pages at different auth0 domains obviously. Since the login url endpoints are saved in the Auth0 admin console, it could be easy to directly check the page. If that doesn't work, you could require customers store the login url's to make scanning them easier.