AgentCore Policy & Temporal Rules: A UK Production Gate for Tool Authorization

Agents choose tools at runtime — UK estates need Gateway policy, not prompt hope

Classic applications enforce order and limits in deterministic code. AI agents decide which tools to call, with which arguments, and in what sequence. A single tool call can look safe in isolation and still be harmful in context — for example after reading untrusted data, or after swapping an ID the previous tool returned.

On 3 March 2026, AWS announced Policy in Amazon Bedrock AgentCore as generally available: centralized, fine-grained controls for agent–tool interactions, evaluated outside agent code. Policies author in natural language (converted to Cedar), live in a policy engine, and attach to an AgentCore Gateway that intercepts tool traffic before allow or deny. Semantics are default-deny and forbid-wins.

This UK playbook is your production gate: Gateway-first tooling, Cedar baselines, then Dogwood temporal policies for trajectory-aware rules.

Cloud AI infrastructure

What AgentCore Policy is — and is not

Principals depend on Gateway auth:

• AgentCore::OAuthUser — from JWT sub, with claim tags (scope, role, …)
• AgentCore::IamEntity — from caller IAM identity / assumed-role ARN

Regions (GA note): thirteen, including Europe (London), Ireland, Frankfurt, Paris and Stockholm — useful for UK residency designs that keep control-plane calls in-region.

What this is not: a replacement for Bedrock Guardrails content filters alone, an excuse to skip IAM least privilege, or a policy that still works if the agent bypasses the Gateway and calls tools directly. Perimeter only protects traffic that actually hits it.

Why temporal policies exist

Stateless Cedar answers: who can call which tool under what input conditions? Temporal (Dogwood) policies answer: given this session's recent trajectory, is this request authorized?

AWS's August 2026 guidance highlights failure modes that pass per-call checks:

• Hallucinated IDs between lookup and transfer
• Runaway loops that burn cumulative spend
• Contradictory approve/deny pairs in seconds
• Stale market or CRM data used for irreversible actions

Common temporal patterns (illustrative — adapt to your tool schema):

1. Workflow sequencing — require prior successful tool responses within a time window before a privileged action
2. Output-to-input integrity — bind current arguments to prior tool outputs
3. Data freshness — require a recent lookup before execute
4. Cumulative caps — session/trajectory spend or call-count ceilings
5. Human approval consumption — one approval event per high-value action
6. Mutual exclusion / progressive trust decay — block contradictory pairs; shrink write rights after idle time

Enforcement modes matter: start LOG_ONLY, prove decisions in logs, then ENFORCE. Do not leave known-risky production paths on LOG_ONLY.

UK production gate checklist

1. Force Gateway for production tools — resource policies / workload allow-lists so SigV4 or JWT runtimes cannot quietly bypass (pair with Gateway target design).
2. Choose principal model — OAuth user-delegated vs IAM workload; document which JWT claims Cedar may trust.
3. Generate schema from tools — let the engine map tools to actions; reject NL-authored policies that fail validation or analysis (always-allow / always-deny).
4. Baseline Cedar — least-privilege tool sets per role; forbid destructive tools by default.
5. Add 2–3 temporal rules on the highest-blast tools only (approval, freshness, cumulative cap).
6. Propagate session IDs — set x-amzn-bedrock-agentcore-policy-session-id deliberately; auto-generated empty sessions defeat trajectory checks. Keep sessions narrow (one concurrent auth request per session).
7. Know the 24-hour look-back — trajectory events older than that drop; policy engine changes invalidate sessions.
8. Evidence pack — LOG_ONLY samples, deny reasons, owner of policy engine, change control when policies update.

14-day UK action plan

Days 1–3 — Perimeter

• Inventory which agents still call tools outside AgentCore Gateway.
• Attach or create a policy engine on the production Gateway in Europe (London) if residency requires it.
• Set enforcement to LOG_ONLY.

Days 4–7 — Cedar baseline

• Author NL → Cedar for role-based tool access; run validation + analysis.
• Map OAuth claims / IAM roles to principals used in policies.
• Fix always-allow findings before any ENFORCE discussion.

Days 8–11 — Temporal pilots

• Pick one high-risk chain (e.g. read → mutate, or amount thresholds).
• Implement sequencing + approval or freshness rules in Dogwood.
• Verify session header propagation in the agent runtime and API gateway.

Days 12–14 — Enforce and govern

• Flip targeted policies / engine to ENFORCE after deny/allow metrics look sane.
• Brief cyber + DPO: what is blocked, what is logged, residual bypass risks.
• Document runbooks for policy updates (expect session invalidation).

Risks and governance

Closing

AgentCore Policy moves UK Bedrock agent estates from "the model usually behaves" to Gateway-enforced, auditable allow/deny — with temporal rules for the trajectory cases IAM alone cannot see. Ship Cedar baselines first, temporal rules on the blast-radius tools second, and treat Gateway bypass as a P1 defect.

If you want a structured AgentCore Policy / temporal gate design for a UK production Gateway, AIATS offers a Free Evaluation conversation — practical, no theatre.

Questions for the architecture review

1. Do all production MCP / tool calls traverse AgentCore Gateway?
2. Which region hosts the policy engine, and does that match residency?
3. OAuth or IAM principals — and which claims are in scope for Cedar?
4. Which three tools warrant temporal rules first?
5. Who owns LOG_ONLY → ENFORCE, and what metric flips the switch?
6. How are policy denials routed into SIEM / incident process?