A by-reference token is a credential that points to token data held elsewhere, usually requiring introspection or lookup before use. This design lowers direct exposure of claims and can improve control over revocation, audience checks, and privacy. It is commonly used when tighter gateway-mediated validation is needed.
Expanded Definition
A by-reference token is a token format whose value is only an identifier or pointer, while the authoritative claims, scopes, and expiry state live in a separate system. In practice, that usually means the receiver must perform token introspection, gateway lookup, or session validation before granting access. This differs from self-contained tokens, which embed claims directly and can be validated offline.
For NHI and agentic AI systems, by-reference tokens are often chosen when teams want tighter revocation, reduced claim exposure, and centralized policy enforcement at the edge. That makes them useful in gateways, API management layers, and brokered access paths where an AI agent or service account should not carry reusable authority in plain sight. Guidance varies across vendors on how much state should remain in the reference system, but the security intent is consistent: reduce token value if intercepted and keep the authoritative decision point under control. See the NIST Cybersecurity Framework 2.0 for the broader access-control and governance context. The most common misapplication is treating a by-reference token like a self-contained bearer credential, which occurs when downstream services skip introspection and trust the pointer alone.
Examples and Use Cases
Implementing by-reference tokens rigorously often introduces added latency and dependency on an introspection service, so organisations must weigh revocation speed and privacy against availability and operational complexity.
- An API gateway issues a short-lived pointer token to an internal service, then validates it against a central authorization service before forwarding the request.
- An AI agent receives a by-reference token for a narrow tool permission set, so the platform can revoke access immediately if the agent behaves unexpectedly.
- A customer-facing integration uses reference tokens for Salesforce-style delegated access, reducing the amount of claim data exposed if the token is intercepted, as seen in incidents like the Salesloft OAuth token breach.
- A security team uses opaque session identifiers for privileged workflows, then checks audience, expiry, and revocation status at a centralized policy point.
- During secret-hygiene reviews, teams compare token handling patterns against the Guide to the Secret Sprawl Challenge and the OAuth guidance in RFC 7662, which defines token introspection for opaque tokens.
Why It Matters in NHI Security
By-reference tokens matter because they change where trust lives. Instead of trusting whatever the token carries, the system trusts the issuer’s live authorization state. That is valuable in NHI environments where service accounts, workload identities, and agent credentials are frequently overused, duplicated, or left active after their intended lifecycle. NHIMG research shows that 91% of former employee tokens remain active after offboarding and 44% of NHI tokens are exposed in the wild, often in tickets, chat tools, or code commits; those realities make revocation and central validation far more important than token format alone.
This is especially relevant in brokered AI and API ecosystems where hidden credentials can outlive their purpose. By-reference tokens support finer-grained control, but only if the introspection endpoint, logging, and revocation workflow are treated as production dependencies. They also fit the operational direction of RFC 9068 and the control expectations expressed in the 2025 State of NHIs and Secrets in Cybersecurity. Organisations typically encounter the need for by-reference handling only after a leaked token must be revoked quickly, at which point token introspection becomes operationally unavoidable to address.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 and OWASP Agentic AI Top 10 address the attack and risk surface, while NIST CSF 2.0, NIST Zero Trust (SP 800-207) and NIST SP 800-63 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Non-Human Identity Top 10 | NHI-02 | Covers token exposure, lifecycle control, and secret handling for non-human identities. |
| NIST CSF 2.0 | PR.AA | Addresses identity proofing and access enforcement through governed authentication decisions. |
| NIST Zero Trust (SP 800-207) | Section 3.4 | Zero Trust relies on continuous verification rather than assuming token possession is enough. |
| NIST SP 800-63 | AAL2 | Assurance levels inform how strongly access tokens and sessions must be protected. |
| OWASP Agentic AI Top 10 | LLM-04 | Agentic systems need constrained tool authority and revocable credentials. |
Issue narrowly scoped, centrally revocable tokens for AI agents and verify them at every tool boundary.
