diff --git a/kong/kustomization.yaml b/kong/kustomization.yaml
index 1d7e17a..c923648 100644
--- a/kong/kustomization.yaml
+++ b/kong/kustomization.yaml
@@ -18,6 +18,7 @@ resources:
   - mcp/ai-mcp-proxy.yaml
   - mcp/openid-connect.yaml
   - mcp/rate-limiting.yaml
+  - mcp/opa.yaml
   - mcp/audit-log.yaml
   - mcp/audit-log-body-capture.yaml
   - mcp/audit-log-body-capture-bindings.yaml
diff --git a/kong/mcp/opa.yaml b/kong/mcp/opa.yaml
new file mode 100644
index 0000000..0a103e4
--- /dev/null
+++ b/kong/mcp/opa.yaml
@@ -0,0 +1,27 @@
+# Authorisation on tool-call parameters, not just the tool name.
+#
+# The ACL answers "may this identity call create-product?". Nothing answered
+# "may it call it with *these* arguments" — and `write` authorises writing, not
+# this particular record. The read cap counts calls, so one call asking for a
+# hundred thousand rows costs the same as one asking for ten.
+#
+# Enforced here rather than in an agent, because an agent that has been talked
+# into something is exactly the case this exists for. The policy lives once, in
+# k8s-platform/opa/policy.rego, and every domain asks the same server.
+apiVersion: configuration.konghq.com/v1
+kind: KongPlugin
+metadata:
+  name: ${NAME}-customers-mcp-opa
+  namespace: ${NAMESPACE}
+plugin: opa
+config:
+  opa_protocol: http
+  opa_host: opa.opa.svc.cluster.local
+  opa_port: 8181
+  opa_path: /v1/data/kong
+  # The decision is about the arguments, so the arguments have to reach the
+  # decision point. Without this OPA sees a method and a path and nothing it
+  # can rule on.
+  include_parsed_json_body_in_opa_input: true
+  include_body_in_opa_input: false
+  include_route_in_opa_input: false
diff --git a/kong/mcp/pluginbindings.yaml b/kong/mcp/pluginbindings.yaml
index 22eca25..0ea608f 100644
--- a/kong/mcp/pluginbindings.yaml
+++ b/kong/mcp/pluginbindings.yaml
@@ -69,3 +69,21 @@ spec:
       group: configuration.konghq.com
       kind: KongRoute
       name: ${NAME}-customers-mcp
+---
+apiVersion: configuration.konghq.com/v1alpha1
+kind: KongPluginBinding
+metadata:
+  name: ${NAME}-customers-mcp-opa-binding
+  namespace: ${NAMESPACE}
+spec:
+  controlPlaneRef:
+    type: konnectNamespacedRef
+    konnectNamespacedRef:
+      name: ${CONTROL_PLANE_REF_NAME}
+  pluginRef:
+    name: ${NAME}-customers-mcp-opa
+  targets:
+    routeRef:
+      group: configuration.konghq.com
+      kind: KongRoute
+      name: ${NAME}-customers-mcp