Hi @novo,
Welcome to the Auth0 Community!
I understand that you’re running into a problem where users are creating multiple profiles with the same email address when logging in with multiple identity providers.
It is possible to block the signup process when a user tries to sign up with an email address that’s already associated with a profile in your tenant, but that would not be the solution I’d suggest. One reason is because it would lead to a confusing experience for the user and you wouldn’t be able to provide them with feedback on why they’re not able to sign up without revealing that there’s already a profile with that email address, which is a security concern.
In my opinion account linking is the way to go here, in part because it provides your users the convenience of authenticating via multiple identity providers. I have an account linking rule that meets the qualifications you’re describing and if you send me a DM I’d be happy to reply with the code for that rule.
I hope this helps!
Thanks,
Matt