FR: Improve auth.createUser to support importing users from a different service #158
Description
After migrating our app from Heroku to a fully hosted Firebase application, we need to migrate our users database and login capabilities to this new Firebase app.
However, we want our migration to be incremental, since our DB contains 400000+ users.
We have been successfully testing this approach manually with firebase-tools's auth:import command. However, since our migration process is meant to be totally automated and executed in a cloud function of our app, firebase-tools cannot be used.
The better way for us to achieve this would be to improve the admin SDK auth.createUser() method, or alternatively add an auth.importUser() method, to support creating an user with the same set of informations than the auth:import command, especially the ability to pass the user's password hash instead of the unencrypted password and a prior creation date.
Ideally, this method would also allow passing the user's login providers, though this can be achieved later using the Node Firebase SDK for now.