Reading a Firebase/Firestore document with Ruby, REST API and Email / password based authentication

importer.rb

# frozen_string_literal: true

# Usage: Importer.new.read
require 'faraday'

class Importer
  AUTH_URL = "https://identitytoolkit.googleapis.com/v1/accounts:signInWithPassword"
  FIREBASE_API_KEY="CHANGE_ME - see the Settings page of your DB"
  FIREBASE_PROJECT_ID="CHANGE_ME - the ID / Name of your Firestore project"
  FIREBASE_USER_EMAIL="CHANGE_ME - the email of your user"
  FIREBASE_USER_PASS="CHANGE_ME - the password of your user"
  DOCUMENT="CHANGE_ME - the document you want to read"

  def initialize
    sign_in
  end

  def read
    uri = "projects/#{FIREBASE_PROJECT_ID}/databases/(default)/documents/DOC#{DOCUMENT}"
    puts JSON.parse(conn.get(uri).body)
  end
  
  private

  def conn
    @conn ||= Faraday.new(url: "https://firestore.googleapis.com/v1/") do |req|
      req.headers['Authorization'] = "Bearer #{@token}"
      req.headers['Content-Type'] = 'application/json'
    end
  end

  def sign_in
    auth = Faraday.post(AUTH_URL) do |req|
      req.params = { key: FIREBASE_API_KEY }
      req.headers['Content-Type'] = 'application/json'
      req.body = { email: FIREBASE_USER_EMAIL, password: FIREBASE_USER_PASS, returnSecureToken: true }.to_json
    end
    auth = JSON.parse(auth.body)
    @token = auth["idToken"]
  end
end

Google documentation is not clear. There are some Firebase gems but I couldn't find anything that could resolve my problem.
I want to read a document stored on Firestore, authenticating by User / Pass, the ones you create on Firebase Authentication.

The solution uses REST API.

I couldn't find any documentation explaining how it should work exaclty. The steps are:

• Authenticate passing email and password to the identitytoolkit.
• Get the returning token.
• Use the token to make Firebase requests as a Bearer token in the header.