kit-policy

A flexible, composable authorization framework for Kit, inspired by Ruby's Action Policy.

[TOC]

Files

File	Description
`.editorconfig`	Editor formatting configuration
`.gitignore`	Git ignore rules for build artifacts and dependencies
`.tool-versions`	asdf tool versions (Zig, Kit)
`LICENSE`	MIT license file
`README.md`	This file
`examples/blog-policy.kit`	Blog authorization example
`kit.toml`	Package manifest with metadata, tasks, and lint configuration
`src/core.kit`	Core authorization helpers
`src/error.kit`	Authorization errors, result types, and failure reasons
`src/main.kit`	Package root module
`src/scope.kit`	Scope, predicate, and pagination helpers
`tests/policy.test.kit`	End-to-end policy behavior tests
`tests/types.test.kit`	Policy type and helper tests

Dependencies

No Kit package dependencies.

Installation

kit add gitlab.com/kit-lang/packages/kit-policy.git

Usage

import Kit.Policy.Core as PolicyCore
import Kit.Policy.Error as PolicyError
import Kit.Policy.Scope as PolicyScope

type Post = {id: Int, author-id: Int, published?: Bool, title: String}
type User = {id: Int, admin?: Bool}
type AuthContext = {user: User}

post-policy = fn(post, ctx, action) =>
  if ctx.user.admin? then
    PolicyCore.allow
  else
    match PolicyCore.resolve-alias action
      | :show -> PolicyCore.allow-if post.published?
      | :update -> PolicyCore.allow-if (ctx.user.id == post.author-id)
      | :destroy -> PolicyCore.allow-if (ctx.user.id == post.author-id)
      | _ -> PolicyCore.no-rule action

post-scope = fn(posts, ctx) =>
  if ctx.user.admin? then
    posts
  else
    posts |>> List.filter (fn(post) => post.published?)

main = fn =>
  user = {id: 1, admin?: false}
  ctx = {user: user}
  post = {id: 1, author-id: 1, published?: true, title: "Hello"}
  posts = [post]

  if PolicyCore.can-with? post-policy post ctx :update then
    println "Can update post"
  else
    println "Cannot update post"

  visible-posts = PolicyScope.scope-with post-scope posts ctx
  page = PolicyScope.paginate 1 10 visible-posts
  info = PolicyScope.pagination-info 1 10 visible-posts

  println "Visible posts: ${page}"
  println "Pages: ${info.pages}"

  err = PolicyError.not-authorized "Post" :update "not the author"
  println (PolicyError.message err)

main

API Overview

Policy.Core

Core helpers for policy functions that return Result Bool PolicyError.

PolicyCore.can-with? policy resource context action
PolicyCore.may-with? policy resource context action

PolicyCore.allow
PolicyCore.deny
PolicyCore.allow-if condition
PolicyCore.deny-if condition
PolicyCore.no-rule action
PolicyCore.allow-or-deny condition resource-name reason action

Pre-check helpers return Option Bool: Some true allows, Some false denies, and None continues to the main rule.

PolicyCore.admin-bypass is-admin? ctx
PolicyCore.owner-check is-owner? resource ctx
PolicyCore.first-pre-check [check1, check2, check3]

Action helpers provide common action groups and aliases.

PolicyCore.crud-actions
PolicyCore.read-actions
PolicyCore.write-actions

PolicyCore.read-action? action
PolicyCore.write-action? action

PolicyCore.resolve-alias :new     # :create
PolicyCore.resolve-alias :edit    # :update
PolicyCore.resolve-alias :delete  # :destroy
PolicyCore.resolve-alias :view    # :show

Policy composition helpers combine several authorization results.

PolicyCore.all-allowed? [result1, result2, result3]
PolicyCore.any-allowed? [result1, result2, result3]

Policy.Scope

Scope helpers filter collections before returning data to a caller.

PolicyScope.scope-with scope-fn items ctx
PolicyScope.filter-by predicate items

PolicyScope.is-owned-by? get-owner-id get-user-id item ctx
PolicyScope.is-published? get-published item
PolicyScope.is-in-state? get-state target-state item
PolicyScope.is-admin-or? check-admin fallback-check ctx item

Predicate combinators are useful for building reusable scope checks.

PolicyScope.both? pred1 pred2 item
PolicyScope.either? pred1 pred2 item
PolicyScope.not-matching? pred item

Pagination helpers are 1-indexed.

page1 = PolicyScope.paginate 1 10 items
pages = PolicyScope.total-pages 10 items
info = PolicyScope.pagination-info 1 10 items

Policy.Error

Error and result types for authorization failures.

type PolicyError =
  | NotAuthorized {resource: String, action: Keyword, reason: String}
  | RuleNotFound {action: Keyword}
  | ContextMissing {field: String}
  | PolicyNotFound {resource-type: String}
  | CustomError String

type FailureReason = FailureReason {
  policy: String,
  action: Keyword,
  details: String
}

type AuthResult =
  | Allowed
  | Denied String

Helper functions are exported from the module, so when imported as PolicyError they are called as module functions.

PolicyError.not-authorized resource action reason
PolicyError.rule-not-found action
PolicyError.context-missing field
PolicyError.policy-not-found resource-type
PolicyError.custom message

PolicyError.message err
PolicyError.kind err
PolicyError.is-not-authorized? err
PolicyError.is-rule-not-found? err

PolicyError.new policy action
PolicyError.with-details policy action details
PolicyError.policy reason
PolicyError.action reason
PolicyError.details reason
PolicyError.format reason

PolicyError.allowed
PolicyError.denied reason
PolicyError.is-allowed? result
PolicyError.is-denied? result
PolicyError.reason result
PolicyError.to-result resource-name action result

Design Notes

Policies are plain functions, so they are easy to test and compose.
Authorization is explicit: helpers return Result Bool PolicyError instead of throwing exceptions.
Scopes are separate from policy checks so list filtering can happen before rendering or serialization.
Common actions use keywords such as :index, :show, :create, :update, and :destroy.
The package is framework-agnostic and can be used with any Kit application code.

Development

Running Examples

Run the blog policy example with the interpreter:

kit run examples/blog-policy.kit

Compile the example to a native binary:

kit build examples/blog-policy.kit && ./blog-policy

Running Tests

Run the test suite:

kit test

Run the test suite with coverage:

kit test --coverage

Running kit dev

Run the standard development workflow (format, check, test):

kit dev

This will:

Format and check source files in src/
Type check examples in examples/
Run tests in tests/ with coverage

Checking Interpreter/Compiler Parity

Run parity checks for examples:

kit parity --failures-only

Generating Documentation

Generate API documentation from doc comments:

kit doc

Note: Kit sources with doc comments (##) will generate HTML documents in docs/*.html.

Cleaning Build Artifacts

Remove generated files, caches, and build artifacts:

kit task clean

Note: Defined in kit.toml.

Local Installation

To install this package locally for development:

kit install

This installs the package to ~/.kit/packages/@kit/policy/, making it available for import as Kit.Policy in other projects.

License

This package is released under the MIT License - see LICENSE for details.

kit-policy v2026.7.12

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