I’m ready to step up the onboarding flow in my existing Flutter headless storefront for Shopify. The first milestone—and highest priority— is Sign in with Phone Number using OTP, and I’d like you to wire it up with Firebase Authentication. Once that piece is solid, we’ll add Sign in with Google and Sign in with Apple so shoppers can choose whatever feels easiest. Here’s what I need delivered: • Phone-number login via Firebase OTP, fully tested on iOS and Android • Google and Apple sign-in hooks that reuse the same customer record logic • Seamless hand-off to Shopify Storefront API so authenticated users land in their existing customer account (or a new one if none exists) • Clean, well-commented Dart code plus a short integration read-me so my team can maintain it The Flutter project is already live, so you’ll clone the repo, drop in the new auth flows, and submit a working pull request. If you’ve connected Firebase Auth to Shopify before—or feel confident you can map the ID tokens correctly—let’s talk.