Agent Gateway ingress — REQUEST_AUTHZ DENY on HTTP header not enforced for Reasoning Engine

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Subject: Agent Gateway ingress — REQUEST_AUTHZ DENY on HTTP header not enforced for Reasoning Engine (:query / :streamQuery)

Hi,

I need help configuring Agent Gateway in Client-to-Agent (ingress) mode. I want to enforce auth by checking a custom HTTP header (AGENT GATEWAY) , and I don’t understand how to make that work on ingress.

What I tried on ingress

I imported this policy successfully (authz-policies describe shows it):

name: ingress-header-authz-policy
policyProfile: REQUEST_AUTHZ
action: DENY
target:
  resources:
    - projects/.../locations/europe-west4/agentGateways/agw-ingress
httpRules:
  - to:
      operations:
        - paths:
            - prefix: /
    when: '!("idp-custom-key" in request.headers && request.headers["idp-custom-key"] == "1234")'

Expected: missing idp-custom-key: 1234 → HTTP 403
Actual: HTTP 200 with and without the header. No entries in networkservices.googleapis.com/gateway_requests for agw-ingress.

Context — same CEL pattern works on egress

On egress (agw-egress), this DENY policy works for A2A:

name: header-authz-policy
target:
  resources:
    - "projects/PROJECT/locations/REGION/agentGateways/GW_NAME"
policyProfile: REQUEST_AUTHZ
action: DENY
httpRules:
  - to:
      operations:
        - hosts:
            - exact: "REGION-aiplatform.googleapis.com"
          paths:
            - prefix: "/v1beta1/projects/PROJECT/locations/REGION/reasoningEngines/RE_ID_TARGET/a2a"
    when: '!("idp-custom-key" in request.headers && request.headers["idp-custom-key"] == "1234")'

Also: Model Armor on ingress (CONTENT_AUTHZ) returns 403 on jailbreak prompts for streamQuery on the same API endpoint — so ingress AGW seems to affect that path, but header DENY does not.

Questions

  1. Is REQUEST_AUTHZ + DENY on request.headers supported on ingress for ADK Reasoning Engine (:query, :streamQuery) when clientToAgentConfig is set?
  2. Why is the policy deployed but not blocking requests and not generating gateway_requests?
  3. Can iap-ingress-authz on ingress (docs: “IAP isn’t supported during ingress”) prevent DENY evaluation?
  4. What is the recommended way to enforce a custom header / API key for clients calling a RE through ingress AGW?

Thank you.

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