Identity-Aware Token Delegation lets one service obtain or pass a token that preserves the original user’s identity or delegated authority when calling another service. Teams should limit who can request delegation, validate audience and scope, and log token exchange paths, because over-broad delegation can expand access across systems.
How token delegation preserves identity across service calls
Identity-Aware Token Delegation is a controlled exchange, not a blind handoff. The calling service presents or receives a token that still carries the original user identity, or a constrained delegated authority, so the downstream service can make authorization decisions on behalf of that user. That preserves accountability while allowing service-to-service work.
The important design point is that the token should represent what the caller is allowed to do, not simply who owns the infrastructure. In practice, that means the delegation path must be explicit, bounded, and auditable so the receiving service can trust the delegated context without treating it as a full credential transplant.
What makes delegation safe enough to use
Identity-aware delegation depends on scope, audience, and policy checks. The delegating service should only exchange tokens for approved targets, with the token audience bound to the intended service and the scope narrowed to the minimum delegated action set. That is what prevents a valid token from becoming a reusable pass across unrelated systems.
It also means the receiving service should not accept delegation just because the token is structurally valid. It must verify that the delegated identity, audience, and claims align with the request being made, and that the token path is one the organisation intended to support. The control is strongest when delegation is explicit in the protocol design rather than inferred from implementation details.
In OAuth-based environments, this is commonly expressed through token exchange patterns and resource-restricted tokens, which is why standards such as RFC 8693: OAuth 2.0 Token Exchange and RFC 8707: Resource Indicators for OAuth 2.0 are useful reference points for practitioners designing on-behalf-of flows.
For service-to-service identity, the adjacent control problem is often whether the token is merely forwarded or actually constrained to the intended resource. A well-designed delegation flow should avoid token passthrough as a habit and instead use audience-bound tokens with a narrow trust boundary.
Where teams usually get it wrong
The main failure mode is over-broad delegation. If a service can mint or forward delegated tokens without strong checks, it can become a proxy for far broader access than the original user intended. That creates lateral access risk across systems, especially when multiple downstream services accept the same delegated token shape.
Another common error is weak logging and poor traceability. If token exchange paths are not recorded, teams can lose the ability to distinguish a legitimate delegated action from an abuse path that piggybacks on valid identity context. That makes incident review harder and can hide privilege expansion until the blast radius is large.
Protocol guidance such as RFC 9700: Best Current Practice for OAuth 2.0 Security and sender-constrained approaches like RFC 9449: OAuth 2.0 Demonstrating Proof of Possession (DPoP) matters here because delegation should be designed to reduce replay and token abuse, not just to enable compatibility between services.
When the same delegation pattern is used in agent or tool orchestration, the risk rises again because the token may authorize actions that the original user did not explicitly review step by step. In those cases, the delegation policy must be tighter than a generic service credential model, because the delegated authority is part of the security boundary.
Risk and Threat Considerations
Identity-aware delegation is valuable because it preserves user context, but it also creates a high-value abuse path if token exchange is too permissive. A compromised service, overly broad scope, or weak audience check can turn a legitimate delegation mechanism into a cross-system access path that looks normal in telemetry.
Failure mechanism: An attacker or misconfigured service abuses token exchange, reuses delegated tokens outside their intended audience, or leverages broad scopes to move from one trusted service to another.
Impact: The organisation can lose containment between systems, expand the blast radius of a single compromised service, and weaken attribution because downstream actions still appear to come from an apparently valid delegated identity.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP API Security Top 10 addresses the attack and risk surface, while NIST SP 800-53 Rev 5, NIST Zero Trust (SP 800-207) and CIS Controls v8 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-53 Rev 5 | IA-9 — Service Identification and Authentication | Covers service-to-service token-based identity and delegated authentication. |
| AC-6 — Least Privilege | Delegated tokens must be constrained to the minimum authority needed. | |
| Recommendation — Enforce authenticated service interactions and validate delegated credentials before acceptance. Limit delegated token scopes and audience to the minimum required access. | ||
| OWASP API Security Top 10 | API5 — Broken Function Level Authorization | Delegation failures can expose functions beyond the caller's intended authority. |
| Recommendation — Check that delegated calls are authorized for the exact function being invoked. | ||
| NIST Zero Trust (SP 800-207) | Never trust, always verify | Token delegation must be continuously verified at each service boundary. |
| Recommendation — Verify every delegated request at the receiving service before granting access. | ||
| CIS Controls v8 | CIS-6 — Access Control Management | Delegation requires controlling which services can request and use shared authority. |
| Recommendation — Restrict which services may request delegated access and review those paths regularly. | ||
Practitioner Guidance
What to verify: Confirm that only approved services can request delegation, that the target audience is enforced on every exchange, and that scopes are narrowed to the minimum set needed for the downstream action. If a service can exchange tokens for more than one business flow, review whether those flows should be separated.
What to measure: Track how often token exchanges occur, which services initiate them, and whether the downstream token set is consistently narrower than the original privilege set. A rising number of exchange paths or unexplained audience variety is often a sign that the delegation model is being stretched.
Practitioner takeaway: Treat identity-aware delegation as a bounded trust mechanism, not a convenience feature, because its security value depends on strict audience control, narrow scope, and auditability of every exchange path.
Related resources from NHI Mgmt Group
- Guide: Agentic AI Identity Guide
- Identity-Aware Token Delegation
- What is the difference between code scanning and runtime identity monitoring?
- Why do remote and hybrid work models increase the need for identity-aware browser controls?
- Why do federated identity, SSO, and context-aware access controls reduce risk in cloud and remote work environments?