OAuth 2.1 Is Here: What Changed, What's Deprecated, and How to Migrate Your App

OAuth 2.1 consolidates OAuth 2.0 and fourteen years of security best-practice RFCs into a single spec, removing the Implicit Grant, Resource Owner Password Credentials flow, and bearer tokens in URL query strings. The guide details four breaking changes, explains the security rationale behind each removal, and provides TypeScript migration paths for production applications.