sec(iac/azure): pull and push ACR with Entra identities, disable the admin account

[cristim]

What

Ported from LeanerCloud/cloud-commitments-cli#2079 (monorepo split); closes reserved-instances-cli#1970 (no equivalent issue exists yet in this repo).

The Azure Container Registry had its admin account enabled, and both sides of the pipeline used it. CI authenticated with the static admin password to push images, and the Container App pulled with the same password stored as a registry-password secret. The deploy workflow also passed it through nonsensitive() at the login step, so the password was printed in plaintext into every Azure deploy log.

Both halves now use Entra identities. CI pushes through its existing OIDC login (az acr login --name ... instead of a docker-login with the admin password), the app pulls with the user-assigned managed identity it already has attached (registry { identity = ... } plus an AcrPull role assignment scoped to the registry), the stored secret is gone, and admin_enabled is now false. The AcrPull assignment moves into the container-apps module via a moved block so the app can depends_on it, since RBAC propagation can lag a fresh apply.

Verification

• terraform fmt -check -recursive across terraform/environments/azure/ and terraform/modules/compute/azure/container-apps/: clean.
• terraform init -backend=false && terraform validate in both directories: Success! The configuration is valid.
• tflint in both directories: no findings.
• pre-commit run --files terraform/environments/azure/build.tf terraform/environments/azure/compute.tf terraform/environments/azure/registry.tf terraform/modules/compute/azure/container-apps/main.tf terraform/modules/compute/azure/container-apps/variables.tf: every applicable hook passed (terraform fmt/validate/lint, trivy config, secret scan).
• Adversarial re-check for this port: confirmed .github/workflows/deploy-azure.yml runs the azure/login OIDC step (line 166) before Terraform Plan/Apply (the step that invokes the build module's az acr login), so the push side's login ordering claim holds in this repo's workflow too. rollback.yml has the equivalent login before its apply.
• No Go tests under terraform/ cover the Azure container-apps module (only the AWS ci-cd-permissions guard has Go tests); GOWORK=off go test ./terraform/... still passes (54 tests, all AWS-side, unaffected by this change).
• terraform plan/apply were not run against real Azure resources, per instructions.

Not verified in this port (needs Azure credentials this environment does not have, same limitation the original PR called out): az acr show --query roleAssignmentMode on the live registry to confirm it hasn't been switched to ABAC repository permissions, which would break both AcrPull and AcrPush. The operator runbook in the original PR (deploy first, then rotate the admin passwords, then disable) still applies and is unchanged by this port.

Review findings from the original PR

CodeRabbit's included review budget was exhausted before it could analyze this PR (its check reported success with zero files analyzed). The original PR was instead reviewed by an independent adversarial pass that approved the diff and corrected the operator runbook's ordering (rotate after deploying, not before, since rotating first invalidates the password the running app still holds and fails pulls for the whole deploy window rather than a single apply). That correction is already folded into the single commit this port carries; nothing was deferred.

Summary by CodeRabbit

• Security
  • Azure Container Apps now use a managed identity to pull images from the container registry, with pull access granted to that identity.
  • Registry admin access is disabled, and builds authenticate to the registry using the caller’s Entra identity. Callers need the AcrPush role to push images.

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📝 Walkthrough

Walkthrough

Azure ACR push login now uses the caller’s Entra identity. Container Apps use their managed identity for image pulls, with an AcrPull grant scoped to the registry. ACR admin access is disabled, and the existing role assignment state address is moved into the module.

Changes

ACR identity authentication

Layer / File(s)	Summary
Caller push login terraform/environments/azure/build.tf	The build configuration uses az acr login with the caller’s Entra identity and documents the required AcrPush permission.
Managed identity image pulls terraform/modules/compute/azure/container-apps/variables.tf, terraform/environments/azure/compute.tf, terraform/modules/compute/azure/container-apps/main.tf	The module accepts the registry resource ID and configures the Container App to use its user-assigned identity for registry authentication. It grants that identity AcrPull access and makes the app depend on the role assignment. The username, password, and registry-password secret configuration are removed.
Registry admin access and state migration terraform/environments/azure/registry.tf	ACR admin access is disabled. A moved block maps the standalone role assignment address to the assignment inside the Container Apps module.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: 🟡 Moderate · up to c5d56

A fresh deployment may need a second apply if pull permissions have not propagated. Confirm ARM-audience authentication and address the first-deployment timing risk before merging.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely summarizes the main changes: using Entra identities for Azure Container Registry pulls and pushes, and disabling the registry admin account.

✨ Finishing Touches

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[cristim]

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Actionable comments posted: 2

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Inline comments:
Review comments at @terraform/modules/compute/azure/container-apps/main.tf:
- Line 227: Update the Container App deployment flow around
azurerm_role_assignment.acr_pull so a fresh deployment waits for the AcrPull
grant to propagate before creating the first private-image revision. Add a
bounded retry or stage the grant before revision creation; preserve the existing
dependency and avoid requiring a manual second apply.
- Line 91: Enable ARM-audience authentication for the Azure Container Registry
in the Terraform configuration used by the Container App’s
`azurerm_user_assigned_identity.container_app` image-pull identity, so the
registry permits authenticated image pulls.

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📥 Commits

Reviewing files that changed from the base of the PR and between bd67009 and c5d56a7.

📒 Files selected for processing (5)

• terraform/environments/azure/build.tf
• terraform/environments/azure/compute.tf
• terraform/environments/azure/registry.tf
• terraform/modules/compute/azure/container-apps/main.tf
• terraform/modules/compute/azure/container-apps/variables.tf

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[cristim]

Independent adversarial review + local verification: MERGE at c5d56a7. Push path: azure/login precedes apply in deploy-azure/rollback, deploy SP's custom role already grants registries/* (no bootstrap re-apply). Pull path: container app pulls with its UAI; AcrPull moved into the module with a moved block adopting the same principal (no replace). No remaining reader of admin creds in arm/, iac/, .github/. terraform fmt/validate/tflint clean in both dirs; all checks green. Caveat (needs Azure creds): registry roleAssignmentMode must not be ABAC repo-permissions. First apply in a fresh env may need a re-run for RBAC propagation (documented).