Fullmakt vs. Auth0: what's the difference for AI agents?

If you’re wiring up AI agents and shopping for “auth,” you’ll quickly run into Auth0 — one of the best-known identity platforms on the web — and you may run into Fullmakt. Both have something to do with letting software prove it’s allowed to act, but they answer different questions. Auth0 asks who is this, and may they log in? Fullmakt asks for this specific agent call, right now — inject the right secret, check the policy, and record what happened. Understanding that split is the fastest way to know which one you need, and when you need both.

What Auth0 is built for

Auth0 (now Auth0 by Okta) is a customer identity platform — CIAM. Its core job is authenticating people into your apps: username and password, social login, single sign-on, multi-factor, and a managed user directory, all behind standard OpenID Connect and OAuth 2.0. If you need a polished login box and somewhere to store user profiles, this is the category leader.

It also handles machine-to-machine access. Through the OAuth 2.0 client-credentials grant, a backend service, daemon, or CLI exchanges a client ID and secret for a short-lived JWT and calls your API as itself — no user involved.

More recently, Auth0 has extended toward agents with Auth0 for AI Agents (its “Auth for GenAI” work). That adds a Token Vault for storing and refreshing third-party API tokens — Google, GitHub, Slack and the like — on an agent’s behalf, asynchronous authorization for human-in-the-loop approval of sensitive actions, and fine-grained authorization for things like RAG pipelines.

The throughline: Auth0 is an identity provider and authorization server. It lives in the control plane, issuing and verifying the tokens that say who someone is and what they’re broadly allowed to do.

What Fullmakt is built for

Fullmakt is a credential broker for AI agents. Instead of issuing a token and stepping back, it sits in the path of every call an agent makes to a real API or tool. That changes what it can do:

• It mints short-lived, scoped credentials for each agent and task — not standing keys.
• It injects the real upstream secret at the edge. The model never sees the production credential; the broker resolves it at call time and adds it to the outbound request.
• It checks policy per call — by endpoint, method, rate, or data class — and blocks anything off-policy.
• It records everything in a cryptographically chained, tamper-evident audit log, so “which agent did what, when, and was it allowed?” has a provable answer.

Fullmakt is MCP- and OAuth-native and is designed to sit on top of whatever identity provider you already use. It lives in the data plane: less “who is this,” more “for this exact request, broker the secret, enforce the rule, and write it down.”

The core difference: control plane vs. data plane

The cleanest way to hold the two in your head:

• Auth0 issues and verifies identity. It answers who — and hands out tokens that prove it.
• Fullmakt brokers and enforces calls. It answers what is this principal allowed to do on this request — and keeps the secret out of the agent entirely.

One is about getting in the door; the other is about what happens on every step once you’re inside.

Side by side

Dimension	Auth0	Fullmakt
Primary subject	Human/customer identity; M2M services; agents via Auth for GenAI	AI agents calling APIs and tools
Where it runs	Control plane — issues and verifies tokens	Data plane — on every agent-to-API call
Where the secret lives	The app or agent holds the issued token (Token Vault stores third-party tokens)	The real upstream secret is injected at call time; the model never holds it
Policy enforcement	Scopes, RBAC, and fine-grained authorization at issuance	Per-call checks (endpoint, method, rate, data class) at the broker
Revocation	Revoke tokens or sessions	Disable the principal or rotate the secret — every future call stops, no agent redeploy
Audit	Logs and monitoring	Cryptographically chained, tamper-evident record of every issuance, call, and revocation
Integration surface	OIDC/OAuth IdP, SDKs, AI-framework SDKs	MCP- and OAuth-native; bring your own IdP

Where they overlap — and where they don’t

It would be unfair to say Auth0 ignores agents. M2M tokens, the Token Vault, and Auth for GenAI all exist precisely because non-human callers are now a first-class problem. If your need is “let an agent obtain and refresh a Google token” or “authenticate the agent as a client,” Auth0 covers it.

The difference is posture. Auth0 is identity-first: it issues credentials and trusts the holder to use them. Fullmakt is enforcement-first: it assumes the agent should never hold the real secret, evaluates each call as it happens, and leaves a tamper-evident trail. These aren’t competing answers to the same question so much as answers to two different questions.

Better together

Because Fullmakt is built to bring your own IdP, the two compose nicely:

1. Auth0 (or any OIDC provider) authenticates the principal — the human, service, or agent — and establishes who’s acting.
2. Fullmakt brokers the agent’s outbound calls — injecting upstream secrets, enforcing least privilege per request, and recording every call.

You keep the identity layer you already trust and add a chokepoint that makes agent access scoped, revocable, and auditable.

Which should you choose?

• Reach for Auth0 when your problem is user or customer identity: login, SSO, MFA, a user directory, or standard machine-to-machine tokens for your own services.
• Reach for Fullmakt when AI agents touch real APIs and you need the secret kept out of the model, least privilege enforced on every call, instant revocation without redeploying agents, and a provable record of what each agent did.
• Use both when you want a trusted identity layer and a broker that enforces and audits what agents actually do with it.

“Auth” turns out to be two jobs. Auth0 is very good at the first — proving who’s there. Fullmakt exists for the second: making sure that, on every single call, an agent does exactly what it’s allowed to and nothing more, without ever holding your secrets.