Put primary user authentication in the enterprise identity stack and place tool authorization in the agent runtime. That separation lets SSO, directory sync, and tenant controls govern the application while the runtime enforces per-tool scopes and execution-time checks. Mixing those layers usually creates policy gaps and unclear accountability.
Where enterprise teams should draw the line between identity and runtime control
For agent tool access, the cleanest split is to let the enterprise identity stack establish who the user is, while the agent runtime decides what the agent may do with a specific tool in a specific moment. That keeps corporate SSO, directory policy, and tenant controls focused on the application boundary, while execution-time checks stay close to the action that could actually create impact.
That separation matters because tool authorization is usually dynamic: the right answer can depend on the user context, the task, the selected tool, the request content, and whether approval is needed before action is taken. If those decisions are pushed into a generic identity layer, the policy often becomes too coarse to express per-tool scope, per-action approval, or step-up checks.
It also helps to think in terms of control ownership. Identity teams should own authentication, federation, and account governance. The agent platform should own tool invocation policy, scope enforcement, and runtime checks that determine whether a call is allowed at that moment. The more clearly those responsibilities are separated, the easier it is to audit a failure and answer who should have prevented it.
Why runtime authorization needs the tool context
Tool authorization belongs in the runtime because the risk is not just that a person signed in, it is that an agent may invoke a high-impact capability at the wrong time or with the wrong scope. The runtime is the only place that can reliably evaluate the live context of the session, the current task, and the exact tool call before the action executes.
That is why AI Agent Authorisation Guide and Authorisation Models Guide are useful reference points here: the core design problem is not just granting access, but selecting the right model for fine-grained decisions that can vary by action, resource, and context. In practice, that often means policy decisions, scope checks, and approval gates sit closer to the agent than to the identity provider.
Identity systems still matter, but they should provide the upstream trust input, not the final answer for every tool call. A user may be authenticated once, yet the runtime still needs to decide whether a file-writing tool, ticketing tool, payment action, or external API call is permitted under the current task. That distinction is what prevents a generic login from becoming blanket authorization.
How teams keep the architecture explainable and auditable
The most defensible pattern is to keep the authentication path and the authorization path visible separately in design and logging. If the agent runtime denies a tool call, the log should say what policy or scope failed. If the enterprise identity stack denies the user, the log should say that the user or session never reached an authorized runtime state.
That separation is also why IAM and IGA Basics fits this question: teams need a stable identity boundary for authentication, entitlement governance, and access review, while the runtime handles delegated authority and execution-time enforcement. When those boundaries blur, investigations become harder because no one can tell whether a bad action came from weak user access, weak tool policy, or both.
For enterprises operating agents at scale, the practical test is simple: if the control is about proving the user, keep it in identity. If the control is about whether a specific tool action should happen now, keep it in the agent runtime. That division also makes it easier to attach evidence, because identity teams can show login and directory controls while platform teams can show scoped tool policy and runtime enforcement.
Risk and Threat Considerations
When tool authorization is mixed into the identity layer, the common failure mode is over-broad access that survives across tools, tasks, or sessions. That creates a policy gap where a properly authenticated user or agent still gets to perform actions that should have been blocked at execution time.
Failure mechanism: Coarse identity policy cannot express per-tool, per-action, or per-task context, so the runtime inherits an authorization decision that is too broad and too sticky for agent behaviour.
Impact: Excess privilege, unclear accountability, and a larger blast radius if the agent is prompted, tricked, or misrouted into using a powerful tool.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Agentic AI Top 10 and OWASP API Security Top 10 address 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 Agentic AI Top 10 | ASI03 — Identity & Privilege Abuse | Agent tool authorization depends on preventing over-broad agent privilege. |
| Recommendation — Enforce runtime tool scopes and step-up checks for sensitive agent actions. | ||
| NIST SP 800-53 Rev 5 | IA-2 — Identification and Authentication (Organizational Users) | Enterprise identity stack should prove the human user before runtime authorization. |
| AC-6 — Least Privilege | Per-tool runtime scopes are a least-privilege decision point for agent actions. | |
| AU-2 — Event Logging | Separating identity and runtime decisions requires auditable logs for each layer. | |
| Recommendation — Use enterprise authentication for user identity and session establishment. Constrain each tool to the minimum privileges needed for the current task. Log identity decisions and tool authorization outcomes separately for attribution. | ||
| OWASP API Security Top 10 | API5 — Broken Function Level Authorization | Tool calls are function-level actions that need execution-time authorization. |
| Recommendation — Authorize each sensitive tool function at runtime before execution. | ||
Practitioner Guidance
What to verify: Confirm that the identity stack only establishes the user and session, while the agent runtime enforces tool scopes, approval gates, and any step-up checks for sensitive actions. If both layers can independently allow the same high-risk tool call, you do not have a clean control boundary.
Decision rule: Put anything that changes by tool, task, or execution context into the runtime. Put anything that should remain stable across applications, including SSO, directory state, and tenant policy, into enterprise identity. That rule scales better than trying to encode dynamic tool behaviour in a general login system.
What good looks like: A reviewer can trace one denied action from identity to runtime without guessing where the decision was made. The enterprise can show who the user was, and the agent platform can show why the tool call was or was not permitted.
Practitioner takeaway: The safest operating model is not “identity versus runtime”, but “identity proves the actor, runtime governs the action.” If a policy must understand the exact tool call, it belongs where the call is executed.
Related resources from NHI Mgmt Group
- How should enterprise teams decide between agent-to-tool governance and application-to-model routing in AI platforms?
- Why is it necessary to address authorization challenges in AI agent deployment?
- How should security teams govern AI agents that can access enterprise systems?
- How should teams think about AI agent privileges?