Build Time Secrets

Build-Time Secrets

Instructions

Build-time secrets (signing keys, store API credentials, Fastlane match passphrases, Sentry auth tokens) are the ones that most often end up committed by accident. Harden the pipeline, not the developer.

1. What's a Build-Time Secret

• Android: upload keystore, key password, key alias password, Play Developer API JSON, Firebase service account.
• iOS: Apple Developer API key (AuthKey_*.p8), App Store Connect issuer ID, fastlane match passphrase, certificates.
• Cross-cutting: Sentry auth token, npm / Maven publish token, release webhook URLs with embedded tokens.

None of these belong in the repo — including in /android, /ios, /fastlane, or encrypted-but-plaintext-in-CI files.

2. .gitignore Discipline

Commit a strict .gitignore before the first push:

# Android signing
*.keystore
*.jks
keystore.properties
key.properties
google-services.json
play-api-key.json

# iOS signing
*.mobileprovision
*.p12
*.p8
AuthKey_*.p8
ios/fastlane/report.xml

# Generic
.env
.env.*
!.env.example
secrets/
*.pem
*.pfx

Provide .env.example / keystore.properties.example with placeholder values so onboarding is clear.

3. Pre-Commit and CI Scanning

Run gitleaks (or trufflehog) as:

• A pre-commit hook.
• A required CI check on every PR.
• A scheduled scan over the full history (for legacy repos).

# .github/workflows/gitleaks.yml
name: gitleaks
on: [pull_request, push]
jobs:
  scan:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with: { fetch-depth: 0 }
      - uses: gitleaks/gitleaks-action@v2
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        with:
          fail: true

Fail the build on findings. Add allow-listed false positives via .gitleaksignore with a comment explaining why.

4. If a Secret Was Ever Committed, Rotate It

History rewrites with git filter-repo / BFG do not undo a leak:

• Any CI caches / mirrors / forks still have it.
• It was likely indexed by a secret scanner within minutes.
• GitHub, GitLab, and others forward leaked credentials to AWS / Stripe / Google who may auto-revoke.

Policy: every commit that ever contained a secret → rotate at the provider, even if the commit was amended or force-pushed away.

5. CI Secret Scopes

GitHub Actions / GitLab CI / Bitrise all support scoped secrets. Apply least privilege:

• Protect environments (production) — require manual approval.
• Restrict secrets to specific workflows (environment: production gating).
• Never expose production signing to PR workflows from forks (pull_request from forks runs without secrets by default; do not bypass this).

jobs:
  release:
    environment: production # gated
    runs-on: ubuntu-latest
    steps:
      - run: echo "Signing..."
        env:
          ANDROID_KEYSTORE_BASE64: ${{ secrets.ANDROID_KEYSTORE_BASE64 }}
          ANDROID_KEY_PASSWORD:    ${{ secrets.ANDROID_KEY_PASSWORD }}

6. Signing Keys

• Android: use Play App Signing so the upload key is not the production key. Losing the upload key is recoverable via Google; losing the production key used to be fatal.
• iOS: fastlane match with a private encrypted git repo plus MFA on the Apple Developer account.
• Back up keys in a dedicated password manager / HSM, not in Google Drive.

7. Handling Files in CI

For keystores / .p8 / .mobileprovision files, store base64 in CI secrets and materialize at runtime:

echo "$ANDROID_KEYSTORE_BASE64" | base64 -d > app/release.keystore
trap 'shred -u app/release.keystore' EXIT

Always delete after the build step. Never upload the key as a build artifact.

8. Audit Trail

• Every access to a production secret should be loggable (CI run URL + commit SHA + actor).
• Rotate on any suspicious access — especially for secrets a terminated employee had.
• Review secrets quarterly: is each one still used? Revoke the rest.

Checklist

• .gitignore blocks keystores, provisioning profiles, .p8, .env, and service-account JSON.
• gitleaks (or equivalent) runs on pre-commit and on every PR, blocking on findings.
• Any secret ever committed is rotated, regardless of history rewrites.
• CI secrets are scoped by environment; fork PRs cannot access production secrets.
• Android uses Play App Signing; iOS uses match with MFA on Apple accounts.
• Signing files are injected at runtime from base64 secrets and shredded post-build.
• A quarterly review exists to revoke unused CI secrets.