Agent identity answers who or what is making the request, while user delegation answers who authorized that action and under what limits. A signed agent request can prove the bot or automation is real, but it does not prove the request is permitted on behalf of a human. Delegation requires scope, audience, expiry, and a reviewable approval record.
Agent identity: who is calling, not who granted the call
Agent identity is about the authenticated caller in the API transaction: the bot, workload, service, or automation presenting itself to the API. That identity can be strong and verifiable, yet still say nothing about whether the action is allowed to happen on behalf of a person. In practice, this is the difference between proving origin and proving authorization.
For API access, that distinction matters because a valid agent credential can establish “this request came from the right automation” without establishing “this automation may act for this user in this context.” If you need a deeper identity model for autonomous software, Agentic AI Identity Guide explains how agent identity, registration, and delegation fit together.
In other words, agent identity is the subject of authentication. It is the basis for trust in the caller, but it is not yet the basis for user-authorized action, scope limitation, or consented delegation.
User delegation: permission to act on behalf of a user
User delegation answers a different question: which user approved the action, what the agent may do, and under what limits. Good delegation is bounded by scope, audience, expiry, and an approval trail that can be reviewed later. The practical point is that delegation narrows authority, while agent identity only establishes the actor making the request.
That separation is why token exchange and “on-behalf-of” patterns are so important in API design. RFC 8693: OAuth 2.0 Token Exchange defines the core delegation pattern for exchanging one token for another with constrained downstream use, and it is often the cleanest way to represent user-approved access without handing the agent the user’s raw credential.
Where delegation is missing or vague, teams often end up with overbroad service credentials, hidden impersonation, or “it worked, so it must be allowed” assumptions. A useful comparison is the OWASP API Security Top 10, because broken authentication and broken authorization failures are exactly where these boundaries are usually exposed in API programs.
Why the distinction matters in real API architectures
The cleanest way to think about the difference is: agent identity authenticates the machine or agent, while delegation authorizes a specific action on a user’s behalf. That means the same API request may require two separate checks, one for caller authenticity and one for delegated entitlement. If the system collapses them into one step, it becomes difficult to tell whether a request is legitimate, over-scoped, or simply replayed by a compromised agent.
For workloads and service-to-service access, this separation is often reinforced with workload identity and short-lived credentials. SPIFFE workload identity specification is a strong example of how systems can establish strong caller identity without treating that identity as equivalent to user consent. That is also why API programs need explicit authorization logic, not just a trusted caller.
In mature implementations, the delegation artifact should be inspectable: who approved it, what resource it applies to, what audience can receive it, and when it expires. If any of those are absent, the design may still be authenticated, but it is not safely delegated.
Risk and Threat Considerations
When agent identity and user delegation are blurred, the main risk is overreach: a valid automation identity can be mistaken for permission to act broadly, or a stolen agent token can be reused beyond the user’s intended scope. That creates a fast path from authentication compromise to unauthorized API action.
Failure mechanism: The system accepts a strong caller identity but fails to enforce delegation boundaries such as scope, audience, expiry, or approval provenance, so the agent can exercise more authority than the user intended.
Impact: Attackers can abuse valid tokens, over-scoped service access, or impersonation flows to read data, modify records, or trigger downstream actions that appear legitimate in logs.
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 sets the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP API Security Top 10 | API2 — Broken Authentication | API access must distinguish caller identity from delegated authority. |
| API5 — Broken Function Level Authorization | Delegation limits which functions an agent may perform on behalf of a user. | |
| Recommendation — Require separate authentication and authorization checks for delegated API actions. Enforce function-level authorization on every delegated API operation. | ||
| NIST SP 800-53 Rev 5 | IA-9 — Service Identification and Authentication | Agent identity is a service/workload authentication problem in API access. |
| AC-3 — Access Enforcement | Delegation requires enforcement of scope and limits after authentication. | |
| IA-5 — Authenticator Management | Delegation depends on short-lived, managed credentials and tokens. | |
| Recommendation — Authenticate agent callers with service identity controls before evaluating delegated rights. Enforce user delegation limits at the authorization layer, not in the client. Manage token lifetimes and revocation so delegated access expires predictably. | ||
Practitioner Guidance
What to verify: Confirm that your API separates caller authentication from user authorization in both the token model and the enforcement layer. If an agent can present a valid credential, that should not automatically grant the user’s rights unless a delegation token or equivalent proof is present.
Decision rule: If the request must act “as the user,” require a bounded delegation artifact with explicit scope, audience, and expiry. If the agent is only performing its own service function, keep the request tied to the agent’s identity and avoid unnecessary impersonation.
Common mistake: Treating a signed or federated agent request as proof of user consent. That is a caller-authentication signal, not a delegation signal.
Practitioner takeaway: The safest API designs make identity prove who is calling and delegation prove who authorized the act, because collapsing those two questions is where privilege creep and unauthorized action begin.
Related resources from NHI Mgmt Group
- What is the difference between application access and agent identity governance?
- What is the difference between agent identity and service account access?
- What is the difference between API keys and OAuth for AI agent access?
- What is the difference between controlling user access and controlling AI-agent access in MCP deployments?
Deepen Your Knowledge
Reviewed and updated by the NHIMG editorial team on September 30, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
