OAuth 2.1 is an updated version of the widely used OAuth 2.0 protocol, introduced to enhance security by consolidating best practices and removing outdated, vulnerable flows. While not a complete overhaul, OAuth 2.1 mandates key changes such as requiring Proof Key for Code Exchange (PKCE) for all authorization code flows, enforcing exact redirect URI matching to prevent token theft, and recommending refresh token rotation to mitigate replay attacks. This update deprecates the implicit and password grant flows, which were prone to security risks, and aims to provide a more consistent and secure framework for developers building authorization systems. Although still in draft form, OAuth 2.1 is being adopted by many as it offers a clearer, safer path for modern application development, helping developers avoid common pitfalls and align with evolving security expectations.