Rego Skill

Rego Policy Development

You are an expert in Open Policy Agent (OPA) and the Rego policy language.

Mandatory Workflow

ALWAYS follow this sequence for any policy task:

1. Understand - Clarify requirements before writing code
2. Generate - Write policy with explicit default deny
3. Test - Create comprehensive *_test.rego with allow AND deny cases
4. Validate - Run opa check and opa test . -v
5. Review - Check against security checklist
6. Iterate - Fix any failures before declaring complete

NEVER skip the test step. Every policy must have tests that pass.

Quick Reference

Core Principles

1. Always Default Deny

Every policy MUST start with explicit default deny:

package mypackage

import rego.v1

default allow := false

allow if {
    # explicit conditions only
}

2. Modern Rego Syntax (OPA 1.0+)

On OPA 1.0+ the if / in / contains / every keywords are built in — no import needed. (import rego.v1 and import future.keywords.* are now no-ops; keep import rego.v1 only if you must also run on OPA 0.x.) See BEST-PRACTICES.md for the full 1.0 migration notes.

package authz
# No import needed on OPA 1.0+.

# Use 'if' for rule bodies
allow if {
    some role in input.user.roles
    role == "admin"
}

# Use 'contains' for set rules
violations contains msg if {
    # condition
    msg := "violation message"
}

# Use 'every' for universal checks
all_valid if {
    every item in input.items {
        item.status == "approved"
    }
}

3. Structured Decisions

Return structured objects for better debugging:

decision := {
    "allowed": allowed,
    "reason": reason,
    "context": {
        "user": input.user.id,
        "action": input.action
    }
}

4. Always Write Tests

Every policy needs a companion *_test.rego file:

package mypackage_test

import rego.v1
import data.mypackage

test_allow_admin if {
    mypackage.allow with input as {
        "user": {"roles": ["admin"]}
    }
}

test_deny_guest if {
    not mypackage.allow with input as {
        "user": {"roles": ["guest"]}
    }
}

Validation Commands

Always validate your work:

# Check syntax
opa check policy.rego

# Run tests
opa test . -v

# Format code
opa fmt -w policy.rego

# Test with coverage
opa test . -v --coverage

Common Patterns

RBAC (Role-Based Access Control)

package rbac

import rego.v1

default allow := false

allow if {
    some role in input.user.roles
    some permission in role_permissions[role]
    permission == required_permission
}

role_permissions := {
    "admin": ["read", "write", "delete"],
    "editor": ["read", "write"],
    "viewer": ["read"]
}

required_permission := "read" if input.action == "GET"
required_permission := "write" if input.action in ["POST", "PUT", "PATCH"]
required_permission := "delete" if input.action == "DELETE"

ABAC (Attribute-Based Access Control)

package abac

import rego.v1

default allow := false

# Owner can do anything with their resources
allow if {
    input.user.id == input.resource.owner_id
}

# Department access
allow if {
    input.user.department == input.resource.department
    input.action in ["read", "list"]
}

API Gateway Authorization

package gateway

import rego.v1

default allow := false

allow if {
    is_public_path
}

allow if {
    is_authenticated
    has_required_permission
}

is_public_path if {
    some pattern in public_patterns
    glob.match(pattern, [], input.path)
}

public_patterns := [
    "/api/health",
    "/api/public/*"
]

is_authenticated if {
    input.token.valid == true
    time.now_ns() < input.token.exp * 1e9
}

has_required_permission if {
    required := path_permissions[input.method][_]
    glob.match(required.pattern, [], input.path)
    some role in input.token.roles
    role in required.roles
}

Security Checklist

Before completing any policy:

• Default deny is explicit (default allow := false)
• No unconditional allow := true
• Input validation for required fields
• Type checking where needed (is_string, is_array)
• No path traversal vulnerabilities
• Tests cover allow AND deny cases
• Tests cover edge cases (null, empty, missing)

Detailed Guides

For comprehensive guidance, see:

• GENERATE.md - Step-by-step policy generation
• SECURITY.md - Security review checklist
• TESTING.md - Test patterns and coverage
• BEST-PRACTICES.md - Performance and style

Example Files

See examples/ directory for complete working examples:

• rbac_test.rego - RBAC with tests
• gateway_test.rego - API gateway with tests

Suite-wide security audit (Workflow)

The generate / test / review loop above handles ONE policy at a time inline. To audit an entire policy corpus for security drift, this skill ships a read-only fan-out workflow: rego-security-audit-workflow.js. It spawns one auditor per .rego policy, scores each against the 10-check rubric below, adversarially verifies every failed check (so a misread doesn't become a false alarm), runs a cross-policy conflict pass over same-package groups, and returns a dated report payload. It is report-only — it never edits a policy. The skill (this wrapper) owns the date and the git write/commit; the workflow owns the fan-out (it's read-only against git).

Requires a Claude Code harness with the Workflow (multi-agent orchestration) tool. The inline generate / test / review loop works without it; only this corpus-audit needs it.

The 10 checks (each cites a SECURITY.md / BEST-PRACTICES.md section)

Conventions are NOT findings. Each policy is judged against ITS OWN idiom. Using import future.keywords instead of import rego.v1, or returning {"allow": bool} instead of a bare allow, is recorded descriptively and never raised as a check failure. Only genuine, exploitable authorization defects are reported.

Running the audit

- [ ] 1. DATE=$(date +%F); ensure <root>/audit-reports/ exists.
- [ ] 2. Run the workflow (background; you're notified on completion).
- [ ] 3. Render the returned payload into <root>/audit-reports/REGO-SECURITY-AUDIT-<DATE>.md.
- [ ] 4. Commit the report to a branch (never the default branch). Do NOT push or open an MR unless asked.
- [ ] 5. Report the headline counts; offer to fix Critical/Medium items via the inline generate/review loop.

Step 2 — invoke:

Workflow({
  scriptPath: "<this-skill-dir>/rego-security-audit-workflow.js",
  args: { date: "<DATE>", policyRoot: "<dir-with-.rego-files>" }   // policyRoot defaults to cwd
  // optional: focus (steer) | policies:[explicit list] | maxPolicies (default 12)
})

The payload is { date, rubricVersion, scope:{audited,total,deferred,baselineTests,maxPolicies,policyRoot}, confirmed:[…severity-sorted, false alarms already dropped…], policyVerdicts:[…], crossPolicy:[…] }. confirmed = findings that survived adversarial verification. crossPolicy = same-package overlapping/shadowed-rule / eval_conflict issues a single-policy auditor can't see.

Date: YOU own the date — use the $DATE you computed for the filename, heading, and commit. If the payload's date reads "(undated)" (args didn't propagate), ignore it and stamp $DATE anyway.

Step 3 — report shape (REGO-SECURITY-AUDIT-<DATE>.md):

# Rego Security Audit — <DATE>

**Scope:** audited <audited> of <total> policies; baseline `<baselineTests>`. **<N> confirmed findings
(<C> Critical), <R> false alarms dropped, <X> cross-policy issues.**

## Confirmed findings (fix these)        <!-- one ### block per item, Critical first -->
### [<severity>/<check>] <policy>
- **Evidence:** <evidence>
- **Rubric:** SECURITY/BEST-PRACTICES <section>
- _verifier:_ <reConfirm>                <!-- or "unverified — confirm manually" if no verdict -->

## Cross-policy issues                    <!-- from crossPolicy[]; omit section if empty -->
### [<severity>/<kind>] <policies>
- <detail>

## Per-policy verdicts
| Policy | Package | Decision shape | Tests | Fails | N/A | Summary |
|--------|---------|----------------|-------|-------|-----|---------|
| … (one row per policyVerdicts entry) … |

If confirmed is empty, still write the report (a clean run is a useful record) and say so.

Step 4 — commit to a branch (never the default branch; no push/MR unless asked).

Incremental mode (optional)

The workflow carries a RUBRIC_VERSION. To audit only changed policies, the wrapper computes the set whose git hash-object differs from the last report's manifest (or all, if RUBRIC_VERSION bumped), and passes them as args.policies. First cut: full-suite every run (small corpora audit fast).

Notes & anti-patterns

• Report-only is the contract. This workflow finds; you fix (via the inline generate/review loop). An unattended agent "fixing" a large gateway policy is worse than a reported finding.
• The verify phase matters. A policy isn't insecure because one agent misread it — every Critical/Medium finding is adversarially re-checked, and false alarms are dropped before the report.
• Sizing: keep a run ≤ ~12 policies / ~50 agents. maxPolicies (default 12) bounds it; deferred policies are listed in scope.deferred and re-surface on a later run.