Supporting Google Account username change in your app- Google Developers Blog

This post explains the technical implications of Google Account username changes for applications integrating with Sign in with Google. It details how subject ID remains stable, while email addresses can change. It outlines potential disruptions for platforms identifying users by email address, especially when OAuth grants are revoked, and recommends using subject ID as the primary identifier, providing email-based account recovery, and enabling email updates for traditional accounts to prevent duplicate accounts and ensure seamless user transitions.