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Suppose an AI agent needs to read one project issue, but it runs with a developer’s token that can also write to a repository or access unrelated services. That is an illustration, not a reported incident: the agent’s practical authority comes from the credential it uses, not from the narrowness of its prompt. If someone else can use that credential, they may be able to exercise the permissions it carries.
Why a token defines an agent’s practical authority
A token is a credential a service checks when a client requests access. With a bearer token, possession can be enough to present the credential; the receiving service still applies its validity checks and authorization rules. NIST warns that “Any person, system, or service that gains access to the token can present it.” A stolen token can therefore become a route to API access, not merely a secret someone has seen.
That risk grows when an agent inherits a human developer’s credential, uses a static API key, or holds a long-lived token with broad permissions. NIST notes that credentials can leak through configuration files, Markdown files, and logs. An agent that reads untrusted content or invokes tools should not be trusted to compensate for those risks through prompt instructions or model alignment: authorization must be enforced by the identity system and the services the agent calls.
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Identity: who is acting?
Give each agent workload an attributable identity of its own rather than reusing a developer’s personal credentials. Separate identities by workload and, where practical, distinguish read-only work from write-capable work. This makes activity easier to attribute and lets operators revoke one workload’s access without necessarily disrupting a person or other workloads. OWASP’s DevSecOps guidance recommends unique agent identities and separate read-only and write-capable identities.
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Scope: which resources and actions are allowed?
Scope describes the resources and operations the credential permits. Start with the tools and access needed for the specific task, not a broad role that might happen to work. For example, reading one issue does not by itself justify repository write access or access to unrelated services. OWASP advises: “Grant agents the minimum tools required for their specific task.” Its guidance also calls for per-tool scopes, such as read-only access or access to specific resources, and explicit authorization for sensitive operations.
OAuth does not guarantee least privilege by itself: a token can still represent a broad role. Review the actual permissions it grants, and enforce authorization at the tool or API boundary. OWASP cautions against relying on a model-context flag alone to approve a sensitive operation; approval belongs in middleware or another enforcement point that controls execution.
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Lifetime: how long can it be used?
A short-lived credential limits the time window in which a copied token can be useful. Issue credentials for the task and only for as long as needed, rather than leaving an agent with a long-lived secret. If an implementation uses refresh tokens, their handling and protection also matter; RFC 9700 says refresh tokens for public clients must be sender-constrained or rotated.
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A token intended for one resource server should not be accepted by unrelated services. RFC 9700 recommends restricting access-token privileges to the minimum required and generally restricting tokens to a specific resource server or a small set. The receiving server should check that the token was intended for it and covers the requested resource and action.
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Sender constraint: which client must prove possession?
A bearer token can generally be presented by whoever obtains it. Sender-constrained tokens add a check: the client must demonstrate possession of associated key material. DPoP and mutual-TLS-bound tokens are examples described in NIST guidance and RFC 9700. This can reduce the usefulness of a stolen token, but it is not a guarantee if an attacker obtains both the token and the associated key material.
A practical sequence for safer agent credentials
- Assign a workload identity. Give the agent its own identity rather than passing through a developer’s personal login or API key. Use separate identities for distinct workloads and, where feasible, separate read-only and write-capable work.
- Allow only the tools and permissions the task needs. Scope access by resource and action, prefer read-only rights when sufficient, and require explicit authorization for sensitive operations.
- Issue a task-specific, short-lived credential. Avoid static, broad credentials in the agent environment. Use an issuance or credential-brokering mechanism that can produce narrowly scoped task tokens.
- Protect credentials during execution. Keep production credentials out of prompts, logs, configuration files, and broadly readable files. OWASP advises treating the process environment, shell history, and
.envfiles as potentially readable by injected instructions; do not assume those locations are safe just because they are not shown in the model’s chat. - Validate at the receiving boundary. The tool or API should verify the token’s identity, audience, resource, and allowed action before executing the request. Put approval for sensitive operations at that execution boundary rather than trusting the agent to self-police.
- Monitor and revoke. Make activity attributable to the workload, watch for unexpected use, and ensure credentials can be revoked or rotated when exposure or misuse is suspected.
What standards and guidance establish
NIST’s agent-identity guidance identifies OAuth 2.0, SPIFFE, JWTs, and X.509 as foundations for identity and credential management, and describes dynamic, tightly scoped, audience-restricted credentials as achievable controls. RFC 9700 likewise recommends minimum privileges, audience restriction, server-side validation, and sender-constraining access tokens. These mechanisms do not remove the need to check what a role permits or to enforce authorization at the service that performs an action.
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NIST IR 8587, published in September 2026, addresses protection of identity tokens, access tokens, and assertions against forgery, theft, and misuse. Its abstract covers key management, token verification, lifecycle controls, and single sign-on, federation, and API access. The report is written for federal agencies and cloud service providers; its existence does not make every recommendation a universal legal requirement.
Review the token as if it had leaked
Ask: if this token appeared in an agent log or were copied from its runtime, what could the holder do, where could it be used, and for how long? Then verify the answers from the token’s actual permissions and the receiving services’ enforcement—not from the task description or the agent’s instructions.
Quick Recap
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- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5 via USB and tap it to authenticate. No batteries, no internet connection, and no extra fees required.
- MOST SECURE PASSKEY: Supports FIDO2/WebAuthn, FIDO U2F, Yubico OTP, OATH-TOTP/HOTP, Smart card (PIV), and OpenPGP. That means it’s versatile, working almost anywhere you need it.
- BUILT TO LAST: Made from tough, waterproof, and crush-resistant materials. Manufactured in Sweden and programmed in the USA with the highest security standards.
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