On Stitch, you can have multiple providers for identity, but then it creates multiple users even with the same email address if you have someone from say Google or then someone who authenticated via email. There is a way to merge two accounts, but it requires the user to authenticate twice and that's not an ideal user experience. One solve is to treat them as one user. The other solve is to create a user metadata collection which both identities can reference, but if you're trying to add rules and permissions you can't put an array of options in the custom user data "user id field." You also can't select multiple databases for different environments. Would be nice if this was more flexible.