I'm researching back-end services to use for a React Native app that I'm looking to develop and I'm currently in between Firebase and MongoDB Stitch. Based on some research, I'm probably going to start development in Firebase given that I've worked with it once before and it will be the quickest to develop in.
However, before deciding I want to ensure that I'd be able to migrate the app to MongoDB in the future if it ever became necessary. Is it possible to migrate users setup with Federated Identification (signed up for an account with Facebook/Google) from Firebase to MongoDB?
Firebase supports export using firebase auth:export to JSON/CSV file. You could then, use mongoimport to migrate the exported users
Here's auth:export docs and here's mongoimport docs