5 open source auth libraries that actually handle AI agents (2026)

I hit this problem a few months back. About 50 agents, each talking to different MCP tool servers, and I couldn't answer a basic question: which agent did what, and who said it could? Most auth libraries didn't help. They were built for humans logging into web apps. Sessions, cookies, redirect flows. My agents don't have browsers. They need their own tokens, scoped permissions, and when one spins up a sub-agent, I need some way to track that chain. Without it you're just staring at logs guessing which agent made which call. I tried five libraries. Here's what I found. TL;DR -- KavachOS is the only one on this list built for agents. Quickstart here. Read on if you want the full picture. At a glance Library Agent identity MCP OAuth Delegation chains Self-host Edge runtime License Better Auth - - - ✅ - MIT KavachOS ✅ ✅ ✅ ✅ ✅ MIT Lucia - - - ✅ - MIT Keycloak - - - ✅ - Apache 2.0 Supabase Auth - - - ✅ - Apache 2.0 Agent capabilities This is where things get thin. Only one library was actual