Add Style Guides section with GitHub Actions, Markdown, and PowerShell guides

Author: MariusStorhaug

src/docs/Style-Guides/GitHub-Actions.md

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+---
+title: GitHub Actions
+description: GitHub Actions style guidelines for consistency and security across workflows and composite actions.
+---
+
+# GitHub Actions style guidelines
+
+This document defines the GitHub Actions style guidelines for all workflow files (`.github/workflows/*.yml`), composite actions (`action.yml`), and reusable workflows in PSModule repositories. These rules follow GitHub Actions best practices and the security guidance enforced by [zizmor](https://github.com/woodruffw/zizmor).
+
+## Scope
+
+- Applies to `.github/workflows/*.{yml,yaml}`, `action.yml`, `.github/dependabot.yml`, and `CODEOWNERS` entries for workflows.
+- Application source code stays out of scope. If a fix requires changes outside `.github/`, surface it as a recommendation instead.
+
+## Naming
+
+- Give every job and every step a `name:` field
+- Use short, human-readable names that describe what the job or step does, not how
+- Keep naming consistent with existing workflows in the repository
+
+**Good:**
+
+```yaml
+jobs:
+  build:
+    name: Build module
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@<sha> # vX.Y.Z
+```
+
+**Bad:**
+
+```yaml
+jobs:
+  build:
+    steps:
+      - uses: actions/checkout@<sha> # vX.Y.Z
+```
+
+## Quoting
+
+- Only quote scalar values when YAML would otherwise misinterpret them
+- Quote values starting with `{`, containing `:`, boolean-like strings (`true`/`false`), or numeric strings
+- Omit quotes everywhere else
+
+**Good:**
+
+```yaml
+run-name: Release ${{ github.ref_name }}
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+```
+
+**Bad:**
+
+```yaml
+run-name: 'Release ${{ github.ref_name }}'
+concurrency:
+  group: '${{ github.workflow }}-${{ github.ref }}'
+```
+
+## Pinning actions
+
+- Pin every `uses:` to a full 40-character commit SHA
+- Add a patch-level version comment (`# vX.Y.Z`) so Dependabot can update SHA and comment together
+- Applies to reusable workflows too (`uses: org/repo/.github/workflows/foo.yml@<sha>`)
+- Exception: first-party actions in the same repository (`uses: ./.github/actions/...`)
+- Resolve SHAs via `gh api` — never invent or guess a commit SHA. Always use the commit SHA, never the annotated-tag object SHA.
+
+**Good:**
+
+```yaml
+- uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+```
+
+**Bad:**
+
+```yaml
+- uses: actions/checkout@v4
+- uses: actions/checkout@main
+```
+
+Resolving SHAs:
+
+```bash
+gh api repos/<owner>/<repo>/git/refs/tags/<vX.Y.Z> --jq '.object.sha'
+# If .object.type == "tag", dereference:
+gh api repos/<owner>/<repo>/git/tags/<sha> --jq '.object.sha'
+```
+
+## Permissions
+
+- Declare workflow-level `permissions:` set to the strictest needed (default `contents: read`)
+- Override per-job when one job needs more
+- Never use `permissions: write-all` or omit `permissions:` entirely
+- Add an inline comment justifying any non-`read` grant
+
+**Good:**
+
+```yaml
+permissions:
+  contents: read
+
+jobs:
+  deploy:
+    permissions:
+      contents: read
+      id-token: write   # OIDC federation to AWS
+```
+
+## Secrets and configuration
+
+- Use `vars.*` for configuration: region, account ID, role ARN, environment name
+- Use `secrets.*` for credentials: API tokens, passwords, signing keys
+- Never hardcode account IDs, role ARNs, or region names
+- Authenticate to cloud providers with OIDC, never long-lived keys
+- In reusable workflows, pass secrets explicitly — never use `secrets: inherit`
+
+**Good:**
+
+```yaml
+permissions:
+  id-token: write
+  contents: read
+
+steps:
+  - name: Configure AWS credentials
+    uses: aws-actions/configure-aws-credentials@<sha> # vX.Y.Z
+    with:
+      aws-region: ${{ vars.AWS_REGION }}
+      role-to-assume: ${{ vars.AWS_ROLE_ARN_CONTINUOUS_DEPLOYMENT }}
+```
+
+**Bad:**
+
+```yaml
+jobs:
+  call:
+    uses: ./.github/workflows/reusable.yml
+    secrets: inherit
+```
+
+## Untrusted input
+
+- Never interpolate untrusted context directly into shell commands
+- Untrusted contexts include `github.event.issue.title`, `.body`, `.comment.body`, `.pull_request.title`, `.pull_request.body`, `.pull_request.head.ref`, `.head_commit.message`, `.review.body`, `.review_comment.body`, and `.head_ref`
+- Pass untrusted values through an `env:` variable and quote them in the shell
+
+**Good:**
+
+```yaml
+- run: echo "Title: $TITLE"
+  env:
+    TITLE: ${{ github.event.issue.title }}
+```
+
+**Bad:**
+
+```yaml
+- run: echo "Title: ${{ github.event.issue.title }}"
+```
+
+## Triggers and isolation
+
+- Default to `pull_request` for PR validation
+- Avoid `pull_request_target` and `workflow_run` unless required — they run with write tokens and secrets while potentially checking out attacker-controlled code
+- If `pull_request_target` is unavoidable, never check out the PR head, or check out into a sandbox without secrets
+- Use `actions/checkout` with `persist-credentials: false` unless the job pushes commits
+
+**Good:**
+
+```yaml
+- uses: actions/checkout@<sha> # vX.Y.Z
+  with:
+    persist-credentials: false
+```
+
+## Runners and concurrency
+
+- Pin `runs-on:` to a specific OS version (`ubuntu-24.04`) over a floating label (`ubuntu-latest`)
+- Add `concurrency:` to deploy and release workflows
+- Use `cancel-in-progress: true` for CI and `false` for deploys
+
+**Good:**
+
+```yaml
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: false
+```
+
+## Operating protocol
+
+Before writing or reviewing a workflow:
+
+1. Read existing workflows and match shell choice, naming, job structure, and comment style
+1. Check `.github/dependabot.yml` for `package-ecosystem: github-actions` and propose adding it if absent
+1. Check `CODEOWNERS` for `.github/workflows/` ownership and recommend it if absent
+1. Resolve SHAs via `gh api` — never invent a commit SHA
+
+## Security checklist
+
+Run mentally (and via [zizmor](https://github.com/woodruffw/zizmor) when available) before declaring done.
+
+### High severity — must fix
+
+- `template-injection` — no `${{ ... }}` from untrusted context inside `run:` or `script:`
+- `dangerous-triggers` — `pull_request_target` / `workflow_run` justified and hardened
+- `unpinned-uses` — every `uses:` has a 40-char SHA and `# vX.Y.Z` comment
+- `excessive-permissions` — workflow- and job-level `permissions:` minimal
+- `secrets-inherit` — no `secrets: inherit`
+- `known-vulnerable-actions` — no pinned versions in GHSA
+- `github-env` — no untrusted writes to `$GITHUB_ENV` / `$GITHUB_PATH`
+
+### Medium severity — fix unless justified
+
+- `overprovisioned-secrets` — no `${{ toJSON(secrets) }}` or wholesale `${{ secrets }}`
+- `cache-poisoning` — no `actions/cache` (or `setup-*` cache) in tag-triggered release workflows
+- `ref-confusion` — pinned ref is not a name shared by both a tag and a branch
+- `ref-version-mismatch` — the `# vX.Y.Z` comment matches what the SHA actually is
+
+### Low severity — fix when reasonable
+
+- `stale-action-refs` — pinned commit corresponds to a real tag
+- `impostor-commit` — pinned SHA exists in the action repo's history
+
+## Related resources
+
+- [GitHub Actions documentation](https://docs.github.com/en/actions)
+- [zizmor — static analysis for GitHub Actions](https://github.com/woodruffw/zizmor)
+- [GitHub Actions Standard](../GitHub-Actions/Standards.md)