simple-authz-v2

A lightweight, secure authorization engine for Node.js using TOON policy files.

Why simple-authz-v2?

Authorization logic scattered across application code looks like this:

if (user.role === 'admin') { ... }
if (user.id === listing.owner_id) { ... }
if (user.permissions.includes('edit_listing')) { ... }

Over time this becomes unmaintainable. simple-authz-v2 moves all authorization rules into a single policy file so your application only ever asks one question:

authz.can(user, 'edit', 'listing', listing)

Features

• TOON v2 policy language — readable, human-auditable .toon files
• Role hierarchy — super_admin extends admin extends editor
• Deny rules — explicit effect: deny always overrides any allow
• Conditions — AND, OR, NOT with full precedence rules
• Zero eval() — conditions evaluated by pure AST tree-walk
• Prototype pollution protection — user/resource inputs are deep-cloned and frozen
• Path traversal protection — load() validates paths against process.cwd()
• TypeScript-first — full .d.ts, zero any in public API
• Dual ESM + CJS — works with import and require
• Audit callback — structured decision logging for compliance
• Deny by default — if no rule matches, access is denied

Installation

npm install simple-authz-v2

Requirements: Node.js 18 or later.

Quick start

1. Create a policy file

# policies/authz.toon

role_hierarchy
  super_admin extends admin
  admin extends editor
  editor extends viewer
end

rule
  role admin
  action *
  resource *
  effect allow
end

rule
  role broker
  action edit
  resource listing
  effect allow
  condition resource.owner_id == user.id AND resource.status == "draft"
end

rule
  role user
  action view
  resource listing
  effect allow
  condition resource.status == "public" OR resource.owner_id == user.id
end

2. Load and check permissions

import { Authz } from 'simple-authz-v2'

const authz = new Authz()
await authz.loadAsync('./policies/authz.toon')

// Simple check
const allowed = authz.can(user, 'edit', 'listing', listing)

// Detailed explanation (for debugging)
const result = authz.explain(user, 'edit', 'listing', listing)
// {
//   allowed: true,
//   reason: 'allow-rule-matched',
//   matchedRole: 'broker',
//   matchedAction: 'edit',
//   matchedResource: 'listing',
//   conditionResult: true,
//   durationMs: 0.12
// }

3. Protect Express routes

app.put('/listings/:id', async (req, res) => {
  if (!authz.can(req.user, 'edit', 'listing', req.listing)) {
    return res.status(403).json({ error: 'Access denied' })
  }
  // proceed
})

API reference

new Authz(options?)

const authz = new Authz({
  // Called after every authorization decision. Errors are swallowed.
  audit: (record: AuditRecord) => logger.info(record),

  // Maximum nesting depth for user/resource objects (default: 10)
  maxContextDepth: 10,
})

authz.load(filePath)

Synchronously load and compile a .toon policy file.

authz.load('./policies/authz.toon')

Throws PathSafetyError if the path resolves outside process.cwd(). Throws ParseError or CompileError on invalid policy content.

authz.loadAsync(filePath)

Asynchronous version of load(). Preferred in production server code.

await authz.loadAsync('./policies/authz.toon')

authz.can(user, action, resource, resourceObject?, extraCtx?)

Returns true if the user is permitted to perform the action. Deny rules always override allow rules. Returns false if no policy is loaded.

authz.can(user, 'edit', 'listing', listing)
authz.can(user, 'view', 'report', report, { tenantId: req.tenantId })

authz.explain(user, action, resource, resourceObject?, extraCtx?)

Returns a detailed AuthzResult explaining the decision. Use for debugging and audit logging. Use can() in hot paths.

const result = authz.explain(user, 'edit', 'listing', listing)
// AuthzResult:
// {
//   allowed: boolean
//   reason: 'allow-rule-matched' | 'deny-rule-matched' | 'condition-failed'
//         | 'no-matching-rule' | 'wildcard-matched'
//   matchedRole?: string
//   matchedAction?: string
//   matchedResource?: string
//   conditionResult?: boolean
//   durationMs: number
// }

authz.validate(filePath)

Validates a .toon file without loading it into the engine. Never throws (except for PathSafetyError — path safety violations are always re-thrown).

const result = authz.validate('./policies/authz.toon')
// { valid: true, errors: [] }
// { valid: false, errors: [{ message, line, column }] }

Policy language (TOON v2)

Rule syntax

rule
  role    <role-name>
  action  <action-name | *>
  resource <resource-name | *>
  effect  <allow | deny>          # optional — defaults to allow
  condition <expr>                 # optional
end

All four fields (role, action, resource) are required. effect and condition are optional.

Effects

# Allow rule (default when effect is omitted)
rule
  role admin
  action *
  resource *
  effect allow
end

# Deny rule — overrides any matching allow rule
rule
  role admin
  action delete
  resource archived_listing
  effect deny
end

Deny always wins. If a deny rule matches, access is denied regardless of any allow rules that also match.

Conditions

Conditions reference three root variables:

# Ownership check
condition resource.owner_id == user.id

# Combined with AND
condition resource.owner_id == user.id AND resource.status == "draft"

# Combined with OR
condition resource.status == "public" OR resource.owner_id == user.id

# Negation
condition NOT resource.archived == true

# Parentheses for grouping
condition (resource.status == "public" OR resource.owner_id == user.id) AND NOT resource.suspended == true

Operator precedence (tightest to loosest):

1. ( ) — grouping
2. == != > >= < <= — comparison
3. NOT — unary negation
4. AND — logical and
5. OR — logical or

Comparison operators: == != > >= < <= All use strict equality — no JavaScript type coercion.

Role hierarchy

role_hierarchy
  super_admin extends admin
  admin extends editor
  editor extends viewer
end

super_admin inherits all rules of admin, editor, and viewer. Inheritance is fully expanded at compile time — zero runtime cost. Cycles are detected and throw a CompileError.

Include directive

Split large policies across multiple files:

include "./policies/listings.toon"
include "./policies/users.toon"

Paths are resolved relative to the file containing the include. Circular includes are detected and throw a CompileError.

Comments

# This is a comment
rule
  role admin   # inline comment
  action *
  resource *
end

TypeScript types

import type {
  User,
  AuthzOptions,
  AuthzResult,
  AuditRecord,
  ValidationResult,
  PolicyError,
  DecisionReason,
} from 'simple-authz-v2'

// User shape
interface User {
  id: string | number
  roles: readonly string[]
  [key: string]: unknown  // any additional fields accessible in conditions
}

// Decision reasons
type DecisionReason =
  | 'allow-rule-matched'
  | 'deny-rule-matched'
  | 'condition-failed'
  | 'no-matching-rule'
  | 'wildcard-matched'

Error types

import {
  AuthzError,      // base class
  ParseError,      // invalid .toon syntax  — has .line, .column, .sourcePath
  CompileError,    // semantic error        — has .sourcePath
  EvaluationError, // condition eval error
  PathSafetyError, // path traversal attempt
  ContextError,    // prototype pollution or bad input shape
} from 'simple-authz-v2'

Audit logging

const authz = new Authz({
  audit: (record) => {
    // AuditRecord shape:
    // {
    //   allowed: boolean
    //   userId: string | number
    //   roles: readonly string[]
    //   action: string
    //   resource: string
    //   reason: DecisionReason
    //   durationMs: number
    //   timestamp: number   // unix ms
    // }
    logger.info({ event: 'authz_decision', ...record })
  },
})

Errors thrown inside the audit callback are silently swallowed and will never propagate to the caller.

Security model

See SECURITY.md for the vulnerability disclosure process.

Migration from v1

See MIGRATION_v1_v2.md for a complete upgrade guide.

The most important change: condition variables now use resource.x instead of the resource type name (e.g. listing.x).

- condition listing.owner_id == user.id
+ condition resource.owner_id == user.id

Contributing

1. Fork the repository
2. Create a feature branch
3. Ensure pnpm ci passes (typecheck + lint + tests + build)
4. Open a pull request

See SECURITY.md before reporting vulnerabilities.

License

Apache 2.0 — © 2025 Dhruvil