chore(iac): low findings from the 2026-09-02 audit: CFN host param, GCP KMS key, dev CORS

[cristim]

Summary

Three low-severity Terraform and CloudFormation findings from the 2026-09-02 audit, grouped because each is a few-line change in the IaC tree and none is tracked elsewhere. Each item is independently actionable; keep the location and scenario with it if splitting any out.

• CloudFormation WIF template makes the operator keep the issuer URL and its condition-key host in sync by hand (A13b-014)

  • Location: iac/federation/aws-target/cloudformation/template.yaml:20-28 (OIDCIssuerHost parameter), :265-267 (condition keys) at 3c0f8ac94048a2c36fce5ccddee54e6c4849a5cd
  • What: OIDCIssuerHost is a second free-text parameter whose own description says it must equal OIDCIssuerURL minus https:// and that keeping them in sync is the operator's job. Its two AllowedPatterns constrain shape only. The Terraform sibling derives the host in one line: iac/federation/aws-target/terraform/main.tf:22 (trimsuffix(trimprefix(var.oidc_issuer_url, "https://"), "/")).
  • Failure scenario: the two values disagree by a trailing slash or a tenant-ID typo. IAM never populates <host>:aud / <host>:sub for the incoming token, StringEquals fails, and every AssumeRoleWithWebIdentity is denied. It fails closed, but after the stack reports success, with no diagnostic naming the mismatch.
  • Fix: remove OIDCIssuerHost and derive it as !Select [1, !Split ["https://", !Ref OIDCIssuerURL]] so one input cannot contradict the other. aws-cfn-deploy.sh.tmpl passes the parameter today (see chore(scripts): generate-federation-iac.go iacData has drifted out of sync with the templates it renders #153), so drop it from the parameter overrides in the same change.

• GCP OIDC signing key is explicitly unprotected where its AWS twin was given create_before_destroy (A13c-024)

  • Location: terraform/modules/compute/gcp/cloud-run/signing-key.tf:24-38 at 3c0f8ac94048a2c36fce5ccddee54e6c4849a5cd
  • What: google_kms_crypto_key.signing sets destroy_scheduled_duration = "86400s" with the comment "tests redeploy often" and an explicit lifecycle { prevent_destroy = false } (Terraform's default, so the line states rather than changes the posture). modules/compute/aws/lambda/signing-key.tf:19-27 carries create_before_destroy = true with a seven-line rationale citing fix(oidc): provision EC P-256 signing keys in Terraform to match ES256 code (follow-up to #882) cloud-commitments-cli#1480: replacing the OIDC signing key destroy-first breaks client-assertion JWT minting. The GCP key has neither mechanism.
  • Failure scenario: a ForceNew change on the key (purpose, version_template.algorithm, or the key ring's location via var.region) in a production project schedules the live signing key for destruction with a one-day window, and every federated target cloud rejects assertions until the new JWKS propagates.
  • Fix: make prevent_destroy and destroy_scheduled_duration module inputs so production gets the protective values and only test environments opt out, and add create_before_destroy = true to match the AWS twin.

• A live Lambda Function URL hostname is hand-maintained in a tracked tfvars file (A13c-017)

  • Location: terraform/environments/aws/github-dev.tfvars:31-34 at 3c0f8ac94048a2c36fce5ccddee54e6c4849a5cd; terraform/.gitignore:12-16 ignores *.tfvars then re-admits !github-*.tfvars
  • What: the Function URL ID is server-assigned and only known after apply, so lambda_allowed_origins carries it pasted by hand, and the comment three lines above says to update it whenever dev is redeployed. The endpoint is a public URL, not a credential.
  • Failure scenario: a redeploy that reissues the URL silently invalidates the CORS allowlist. The failure surfaces as a browser CORS error, not as a Terraform diff.
  • Fix: supply the origin from the deploy workflow via TF_VAR_lambda_allowed_origins, reading the previous apply's function_url output, instead of committing the host. sec(iac): flip dev/staging/prod to AWS_IAM + enable CloudFront OAC (runtime cut-over for #424) #16 (CloudFront cut-over) would replace this origin with a stable domain and make the item moot; fix here only if sec(iac): flip dev/staging/prod to AWS_IAM + enable CloudFront OAC (runtime cut-over for #424) #16 stays parked.

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Found by the 2026-09-02 codebase audit, findings A13b-014, A13c-024, A13c-017, reported by one reviewer and independently confirmed by a second. Full report: docs/audits/codebase-audit-2026-09-02.md.