Arandu Policy and Grants

What it does

When your agent uses it

• Writing or changing who may read or change a record in an Arandu app
• Fixing a compile error that asks for a security.Grant
• Adding tenant isolation to a new service or Model query
• Writing a Policy for a new resource

Example prompts

• “Add a Policy so only an invoice's owner can update it, and wire it into the service.”
• “InvoiceService.Get will not compile without a Grant. What should I do?”
• “Make sure this report endpoint is tenant-isolated and re-authorizes each row.”

Requirements

• An Arandu Go project

Workflow steps

5 steps, taken from the first numbered list in SKILL.md.

1. 1Name the action as a constant in the policy's file, beside the five
2. 2Decide in Can, inside the custom block: tenant isolation first, the
3. 3Ask from the service, twice for one row. Once with the zero value, to
4. 4Read and write with the Grant that came back. Reads are not exempt: a
5. 5For work with nobody asking, use auth.SystemGrant in a seeder, a job, a

What it can do on your machine

Read from SKILL.md and the folder at commit b8a4273. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • go
  • bash

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Arandu Policy and Grants loads about 1.9k tokens when it runs. Until then it costs about 154 tokens; SKILL.md has 813 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~154

When it runs · the whole SKILL.md, loaded when a task matches

~1.9k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from arandu-io/arandu at commit b8a4273, republished under its MIT licence (© arandu-io). 813 words, ~1,904 tokens.

name

arandu-policy

description

Authorization in an Arandu (Go) application. Use when writing or changing who may read or change a record, when a Model or service call will not compile, when something asks for an auth.Grant, or when the request mentions "permissions", "roles", "who can access", "only the author", "authorize", "multi-tenant", "tenant isolation", or "this method needs a Grant". Also use when tempted to remove a parameter to make code compile -- here that parameter is the only thing making the query safe. Covers Policy, Grant, auth.Authorize, auth.Tenant, re-authorizing the row, SystemGrant and aru make:policy.

license

MIT

package example

import (
	"context"
	"fmt"

	"github.com/arandu-io/hesape/auth"
	"github.com/arandu-io/hesape/database"

	models "<module>/app/Models"
)

// NotePin is pinning one note.
const NotePin auth.Action = "note.pin"

// PinPolicy decides who pins a note: its author, in its tenant.
type PinPolicy struct{}

var _ auth.Policy[models.Note] = PinPolicy{}

// Can answers nil to allow and an error to deny, and denies by falling through.
func (PinPolicy) Can(_ context.Context, s auth.Subject, a auth.Action, n models.Note) error {
	if n.ID != "" && n.TenantID != s.Tenant {
		return fmt.Errorf("note belongs to another tenant")
	}
	if s.ID == "" || s.Tenant == "" {
		return fmt.Errorf("pinning needs somebody signed in")
	}
	if a == NotePin && (n.ID == "" || n.OwnedBy(s.ID)) {
		return nil
	}
	return fmt.Errorf("no rule allows %s on note", a)
}

// Pin reads the row through a Grant, authorizes the row it read, and writes
// with the Grant that decision issued.
func Pin(ctx context.Context, db *database.DB, actor auth.Subject, id string) error {
	g, err := auth.Authorize(ctx, PinPolicy{}, actor, NotePin, models.Note{})
	if err != nil {
		return err
	}
	note, err := models.Notes(db).FindOrFail(ctx, g, id)
	if err != nil {
		return err
	}
	g, err = auth.Authorize(ctx, PinPolicy{}, actor, NotePin, *note)
	if err != nil {
		return err
	}
	note.Pinned = true
	_, err = note.Save(ctx, g)
	return err
}

export GOWORK=off
aru model:build --check
aru view:build
gofmt -l $(find . -name '*.go' -not -path '*/testdata/*' -not -name '*.kyse.go')
go vet ./...
bash tests/test-layout-guard.sh
go test -race ./...
go build ./...
aru doctor

<!-- arandu:begin custom -->

<!-- arandu:end custom -->

© arandu-io, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .agents/skills/arandu-policy of arandu-io/arandu.

Open the folder on GitHubat commit b8a4273