feat: complete security baseline and secure configuration

[lahiruudayakumara]

Summary

Completes the foundation security baseline with an actionable threat model, fail-closed production configuration, data-protection rules, hardened HTTP responses, CI security gates, and governed risk exceptions.

Closes #17

Changes

Threat model and data protection

• Document protected assets, authorized and hostile actors, and trust boundaries
• Threat-model taxpayer, officer, administrator, integration, database, queue, document, observability, and deployment paths
• Define abuse cases, mitigations, detection signals, and residual deployment risks
• Classify secrets, taxpayer data, financial records, security evidence, internal configuration, and public information
• Define encryption, access, logging, retention, legal-hold, export, backup, and disposal requirements

Secure configuration

• Require an explicit development, test, or production environment
• Fail production startup unless TLS termination is confirmed
• Require production secrets through absolute injected-file references
• Reject raw production database, OIDC, object-storage, and SMTP secrets
• Apply the same configuration validation to the API, worker, and scheduler
• Add a credential-free production configuration template

Runtime hardening

• Add and test:
  • Strict-Transport-Security
  • Content-Security-Policy
  • Permissions-Policy
  • X-Content-Type-Options
  • X-Frame-Options
  • Referrer-Policy
  • Cross-Origin-Opener-Policy
  • Cross-Origin-Resource-Policy
  • Cache-Control: no-store
• Continue using the minimal non-root runtime container

CI and supply-chain security

• Validate secure configuration and exception policy in CI
• Scan source for vulnerabilities, secrets, and IaC misconfiguration
• Retain existing dependency, license, CodeQL, and container scanning
• Generate and scan source and image SBOMs
• Retain SBOM artifacts for security investigations
• Continue requiring commit-pinned GitHub Actions and committed dependency lockfiles

Security exceptions and incident response

• Define a machine-validated security-exception format
• Require an accountable owner, expiry date, affected controls, compensating controls, and recorded risk acceptance
• Reject incomplete or expired exceptions in CI
• Require security-maintainer review through CODEOWNERS
• Prohibit exceptions for cross-tenant access, secret exposure, authentication bypass, ledger integrity, and audit immutability failures
• Expand private vulnerability reporting, evidence preservation, notification, and exercise guidance

Verification

make security-baseline
make go-format-check go-lint go-test
go build ./...
go tool actionlint .github/workflows/security.yml .github/workflows/container-build.yml
bash scripts/ci/validate-workflows.sh

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Review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 987dfba and e119119.

📒 Files selected for processing (36)

• .env.production.example
• .github/CODEOWNERS
• .github/PULL_REQUEST_TEMPLATE.md
• .github/workflows/container-build.yml
• .github/workflows/security.yml
• Makefile
• apps/api/cmd/api/main.go
• apps/api/http.go
• apps/api/http_test.go
• apps/scheduler/cmd/scheduler/main.go
• apps/worker/cmd/worker/main.go
• database/migrations/000002_audit_outbox_observability.up.sql
• database/queries/outbox.sql
• deploy/observability/openrevenue-alerts.yml
• deploy/observability/openrevenue-dashboard.json
• docs/architecture/event-architecture.md
• docs/operations/observability.md
• docs/operations/runbooks.md
• docs/security/data-protection.md
• docs/security/incident-response.md
• docs/security/secrets-management.md
• docs/security/secure-development.md
• docs/security/threat-model.md
• internal/platform/application/metrics.go
• internal/platform/application/ports.go
• internal/platform/application/unit_of_work.go
• internal/platform/application/unit_of_work_test.go
• pkg/config/security.go
• pkg/config/security_test.go
• pkg/middleware/middleware.go
• pkg/middleware/observability_test.go
• pkg/problem/problem.go
• scripts/ci/validate-security-baseline.sh
• scripts/dev/validate-config.sh
• security/exceptions/README.md
• security/exceptions/template.yml.example

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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