🔗 OAuth 2.0 vs OAuth 2.1: what changed, why it matters, and how to upgrade

OAuth 2.0 has been the backbone of modern authentication for over a decade, powering everything from logging into apps to connecting enterprise systems. But OAuth 2.0’s biggest strength—its flexibility—has also been its greatest weakness. By giving developers too many choices, the spec left room for risky flows and insecure defaults that often led to bad implementations.

OAuth 2.1 is here to fix that. While still technically indraft form as of April 2025, it’s already being adopted in production by leading organizations. Anthropic, for example, has made OAuth 2.1 a foundational part of theModel Context Protocol (MCP), which governs how AI agents securely access external tools and data. That’s a glimpse of the future, but the real story is that OAuth 2.1 makes secure implementations easier and safer for everyone, across web apps, APIs, and beyond.