This article provides an in-depth tutorial on implementing authentication using Google sign-in for cross-platform applications developed with Flutter. It also explores the Open ID Connect functionality of Supabase Auth, which allows third-party applications to request users' personal information. The tutorial covers setting up a Flutter project, configuring Google sign-in on Supabase Auth, and creating two screens: LoginScreen and ProfileScreen. The LoginScreen presents a single sign-in button for the user to perform Google sign-in, while the ProfileScreen displays some of the obtained information.