I'd like to introduce you to a new FREE way of building APIs to move your data around without having to go into the headache that is backend development.
It's as easy as 'Select * from users where email = $email'. Any postgreSQL query can be templated with variables, and converted into an API in a matter of seconds.
Any PostgreSQL query can be templated with $variable notation, users can be identified with $sub and $email (Auth0) and then converted into an API.
With MongoDB simply create a valid Mongoose Schema and click a few buttons to create a publicly hosted API.