Memory hook: No embedded keys; authorize every boundary.
Must remember
- Application Default Credentials locate credentials from the execution environment; they are not a permission grant. Use attached service accounts in managed runtimes and Workload Identity Federation for supported external/Kubernetes identities.
- Use OAuth access tokens for supported APIs and audience-bound ID tokens for authenticated service invocation where required. Verify JWT issuer, audience, expiry and signature rather than only decoding it.
- Secret Manager stores versioned secrets; Cloud KMS manages cryptographic keys. Rotate credentials with client coordination and grant only the required secret versions/operations.
- IAP provides identity-aware access to supported applications. Private connectivity, Direct VPC egress, service mesh and Kubernetes NetworkPolicy address different network layers; none replaces application authorization.
- Scan dependencies and container images with supported artifact/security tools. Binary Authorization can enforce deployment policies based on attestations and trusted build evidence.
- Use organization and retention policies intentionally, constrain service identities, and validate input/output at every external boundary. AI-generated code and MCP tools require the same review and privilege limits as other code.
Choose under exam pressure
| Requirement | Choice and reason |
|---|---|
| A CI system outside Google needs short-lived access | Workload Identity Federation instead of a downloaded service-account key. |
| Only approved images may deploy | Trusted build attestations and Binary Authorization policy. |
Traps
- ADC does not mean credentials have the correct role.
- An internal endpoint can still be called by an overprivileged compromised workload.
Active recall
1. What is the difference between Secret Manager and KMS?
One stores secret values; the other manages keys and cryptographic operations.
2. Why check token audience?
A token issued for another service must not be accepted as authorization here.
3. Does a vulnerability scan authorize deployment?
No; policy and risk decisions determine whether the artifact is acceptable.
4. What protects pod-to-pod traffic boundaries?
Supported Kubernetes NetworkPolicies and network design, with identity controls where needed.
5. Why avoid persistent service-account keys?
They are portable long-lived credentials that are difficult to constrain after disclosure.