kit-policy

# kit-policy

A flexible, composable authorization framework for Kit, inspired by Ruby's [Action Policy](https://actionpolicy.evilmartians.io/).

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[TOC]

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## Files

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

## Dependencies

_No Kit package dependencies._

## Installation

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

## Usage

```kit
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`.

```kit
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.

```kit
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.

```kit
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.

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

### Policy.Scope

Scope helpers filter collections before returning data to a caller.

```kit
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.

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

Pagination helpers are 1-indexed.

```kit
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.

```kit
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.

```kit
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:

```console
kit run examples/blog-policy.kit
```

Compile the example to a native binary:

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

### Running Tests

Run the test suite:

```console
kit test
```

Run the test suite with coverage:

```console
kit test --coverage
```

### Running kit dev

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

```console
kit dev
```

This will:
1. Format and check source files in `src/`
2. Type check examples in `examples/`
3. Run tests in `tests/` with coverage

### Checking Interpreter/Compiler Parity

Run parity checks for examples:

```console
kit parity --failures-only
```

### Generating Documentation

Generate API documentation from doc comments:

```console
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:

```console
kit task clean
```

**Note**: Defined in [kit.toml](https://gitlab.com/kit-lang/packages/kit-policy/-/blob/main/kit.toml).

## Local Installation

To install this package locally for development:

```console
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](https://gitlab.com/kit-lang/packages/kit-policy/-/blob/main/LICENSE) for details.