Security

Terraform Branch Deploy combines Branch Deploy's IssueOps controls with Terraform-specific saved plan handling. Treat the two layers separately when reviewing a workflow.

IssueOps Security Model

Use issue_comment for Terraform Branch Deploy workflows:

on:
  issue_comment:
    types: [created]

Issue comment workflows run from the workflow file on the default branch. A pull request author cannot change the deployment workflow in the same pull request and then trigger that changed workflow by commenting on the PR.

Do not use pull_request_target for Terraform Branch Deploy. That trigger is privileged and is intended for narrow PR metadata automation. It must not be combined with checking out or running pull request code.

Keep the job guarded so plain issue comments do not run deployment logic:

jobs:
  deploy:
    if: github.event.issue.pull_request

Inherited Branch Deploy Controls

Branch Deploy handles who can issue commands and when a command may continue.

Do not bypass the state exported by trigger mode. Later steps should use TF_BD_CONTINUE, TF_BD_REF, TF_BD_ENVIRONMENT, and TF_BD_OPERATION instead of re-parsing the comment or inventing a checkout ref.

Recommended production-oriented defaults:

- uses: scarowar/terraform-branch-deploy@<terraform-branch-deploy-ref>
  with:
    mode: trigger
    github-token: ${{ secrets.GITHUB_TOKEN }}
    disable-naked-commands: true
    checks: all
    outdated-mode: strict
    update-branch: warn

For smaller repositories, checks: required can be appropriate when branch protection defines the release gates.

GitHub Actions Hardening Baseline

Follow GitHub's secure-use guidance for every workflow that can deploy infrastructure:

• Keep GITHUB_TOKEN permissions explicit and scoped to the job.
• Pass PR-controlled values through env, action inputs, or CLI arguments; do not interpolate event or comment values directly into shell scripts.
• Write values to GITHUB_ENV and GITHUB_OUTPUT with the multiline file-command format when values can contain arbitrary text.
• Pin third-party actions to a full commit SHA in production workflows.
• Avoid self-hosted runners for public or untrusted pull request deployments unless they are isolated and disposable.
• Review workflow logs after valid and invalid commands to confirm secrets and Terraform variables are not printed.

Terraform Saved Plan Controls

Terraform Branch Deploy handles the Terraform execution path after Branch Deploy allows a command to continue.

Saved plan files and metadata are restored from GitHub Actions cache. The cache key includes the saved plan params hash, and apply refuses a restored plan if the key and metadata disagree. The cache is not an independent tamper-proof artifact store.

Plan Before Apply

Normal apply should be:

.plan to prod
.apply to prod

The saved plan is tied to the environment and commit SHA. If new commits are pushed, run the plan again. If you run another successful plan for the same environment and commit, that newer saved plan supersedes the older one.

Targeted plans follow the same rule:

.plan to prod | -target=module.database
.apply to prod

The apply restores the saved targeted plan. It does not create a fresh plan.

PR comment -var-file values must stay inside the environment working directory after path and symlink resolution. Use relative paths and do not use absolute paths or .. traversal.

Rollback

Rollback uses the stable branch:

.apply main to dev

Rollback is intentionally separate from normal apply. It applies the stable branch directly and does not require a saved pull request plan.

Rollback does not accept Terraform arguments such as -target. A targeted apply is not a reversible Terraform operation; there is no deterministic "undo only this target" command. When recovery must be narrow, create a fix PR and use the normal saved-plan flow.

Workflow Permissions

Use the least permissions that still support comments, checkout, deployments, locks, and checks:

permissions:
  contents: write
  pull-requests: write
  issues: write
  deployments: write
  checks: read
  statuses: read

Add id-token: write when cloud credential setup uses GitHub OIDC.

Grant admin bypass sparingly. Prefer named users or a narrowly scoped team, and protect any admins-pat secret.

Checkout and Credentials

A workflow may do an initial default-branch checkout before trigger mode so the action can read .tf-branch-deploy.yml. Do not check out the target ref or configure cloud credentials until Branch Deploy accepts the command:

- uses: actions/checkout@v6
  if: env.TF_BD_CONTINUE == 'true'
  with:
    ref: ${{ env.TF_BD_REF }}

# Configure cloud credentials here.

This keeps cloud credentials behind Branch Deploy's command, permission, check, and lock decisions.

GitHub Token Isolation

The github-token input is used for Branch Deploy, PR comments, deployments, and lifecycle cleanup. Terraform subprocesses do not receive that token as GITHUB_TOKEN.

If Terraform itself needs to call the GitHub API, provide a separate, least-privileged credential only after trigger mode has accepted the command.

For production workflows, pin third-party actions such as actions/checkout and cloud authentication actions by full commit SHA. For Terraform Branch Deploy itself, use the exact release tag or full commit SHA you reviewed. Use the moving v0 tag only when you intentionally want automatic updates within the v0 release line.

Branch and Fork Settings

Repository Rulesets

Branch Deploy assumes the repository has a release discipline around the stable branch. Protect the default branch or matching ruleset before relying on deployments for production infrastructure.

Recommended ruleset checks:

• Prevent force pushes and branch deletion on the stable branch.
• Require pull requests before merging to the stable branch.
• Require current status checks before merge.
• Dismiss stale approvals when new commits are pushed.
• Require code owner review when ownership matters.
• Use required deployments when your release process depends on GitHub environments.

Locks

Use locks during maintenance or incident response:

.lock prod
.wcid
.unlock prod

By default, deployment locks are released after completion. Use sticky-locks: true only when a person should release the lock manually.

Production Promotion

Mark production environments in .tf-branch-deploy.yml:

production-environments: [prod, prod-eu]

Use Branch Deploy controls for stricter production flow:

with:
  enforced-deployment-order: "dev,staging,prod"
  deployment-confirmation: true
  deployment-confirmation-timeout: 300

Practical Checklist

• Use disable-naked-commands: true.
• Require CI with checks: all or checks: required.
• Keep outdated-mode: strict for production.
• Do not run Terraform Branch Deploy on forked pull requests.
• Keep allow-sha-deployments: false unless there is a specific operational need.
• Limit admins and protect any admins-pat secret.
• Define every production target in production-environments.
• Run .plan to <env> again after new commits.
• Use .apply main to <env> only for rollback.