Where does Agent2Agent fail if teams rely only on logging and not authorisation?

Why logging cannot replace authorisation in Agent2Agent execution

Agent2Agent breaks when teams treat logs as the control boundary instead of the policy boundary. Logging is retrospective: it can reconstruct what happened, but it cannot decide whether an agent was allowed to act with a given token, scope, audience, or delegation chain. In delegated systems, that distinction matters before the action executes.

The failure mode is especially clear when one agent can invoke another, because the second agent may inherit trust from the first without ever being explicitly authorised for that specific operation. The correct question is not whether activity is visible, but whether the request was permitted at the moment of issuance and whether the delegated authority matched the task.

That is why authorisation models need to sit in front of execution, not beside the audit trail. Authorisation Models Guide is useful here because Agent2Agent traffic is ultimately an access decision problem: policy, context, and least privilege have to shape what the agent can do before any downstream tool call is made.

What the missing control looks like in a delegated agent chain

In practice, the gap shows up when a token is valid but too broad, when the audience claim does not match the receiving agent, or when the delegation path is accepted without a policy check. Those failures are easy to miss if teams only review observability records after the fact, because the logs still make the exchange look legitimate.

Multi-step delegation makes this more fragile. If an upstream agent can pass authority onward without a per-hop policy decision, the system can drift from “this actor may request work” to “this actor may authorise work on behalf of others,” which is a much larger trust claim. Multi-Agent and A2A Security Guide is relevant because it treats signed agent identity, delegation chains, and containment as first-class security mechanics, not logging concerns.

Where teams need a concrete implementation frame, the issue is the same one that appears in delegated identity flows: the system must validate the scope and audience before it allows the request to progress. RFC 8693: OAuth 2.0 Token Exchange matters because it formalises token exchange for delegation and makes clear that on-behalf-of execution depends on controlled delegation, not after-the-fact attribution.

Why observability is still necessary, but only after prevention

Logging remains important because it gives attribution, timelines, and forensic evidence when something goes wrong. It also helps compare intended versus actual behaviour, which is useful for incident review and policy tuning. But it is a secondary control: if the request was never authorised correctly, the log only records a policy failure that already happened.

That creates a common operational trap. Teams often invest in richer telemetry while leaving the pre-issuance decision implicit, static, or inherited from a human approval path that does not reflect agent autonomy. In agentic environments, that is not enough, because the security decision must be made at the point where the agent requests or receives authority.

For teams formalising this boundary, AI Agent Authorisation Guide gives a practical model for task-scoped access, per-action policy decisions, and human approval gates where appropriate. Paired with AI Agent Observability, Audit and Incident Response Guide, it reflects the right sequence: authorise first, observe continuously, and use logs to verify and investigate, not to decide whether the action should have been allowed.

Risk and Threat Considerations

When teams rely on logs alone, the risk is not just poor visibility, it is preventable misuse of delegated authority. A compromised or over-permissioned agent can still execute valid-looking requests, and the audit trail will only show the abuse after the damage path has already started.

Failure mechanism: The system treats post hoc telemetry as a substitute for pre-execution policy, so overly broad scopes, wrong audiences, or unchecked delegation chains remain usable until someone reviews the records.

Impact: That creates avoidable blast radius, delayed containment, and a false sense of control, because the environment can be observable while still being openly abusable.

Practitioner Guidance

What to prioritise: Put the authorisation decision at the same control point that issues or accepts delegated execution, and make the decision specific to the action, target, and context rather than to the agent as a whole.

What to verify: Confirm that every agent-to-agent request has an explicit policy check for scope, audience, and delegation path, and that the receiving system can reject a valid token when the requested action exceeds the granted authority.

Common mistake: Treating audit logs as proof of entitlement. Logs prove that an action occurred; they do not prove that the action was authorised, narrowly scoped, or appropriate to the receiving agent.

Practitioner takeaway: In Agent2Agent systems, observability is evidence, not permission, and the security boundary must be the authorisation decision that happens before the first delegated action runs.

Related resources from NHI Mgmt Group

• How should security teams govern machine identity credentials in agentic AI environments?
• How should security teams manage permissions for AI agents?
• How should teams govern AI agents that use MCP?
• How should security teams govern AI agents that use OAuth access?