@conte-ltd/trpc-shield

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tRPC Shield

tRPC permissions as another layer of abstraction!s!
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Table of Contents

1. Overview
2. Installation
3. Usage
4. Documentation
5. Contributors
6. Contributing
7. Acknowledgments

Overview

tRPC Shield helps you create a permission layer for your application. Using an intuitive rule-API, you'll gain the power of the shield engine on every request. This way you can make sure no internal data will be exposed.

Installation

Using npm

npm install @conte-ltd/trpc-shield

Using yarn

yarn add @conte-ltd/trpc-shield

Usage

• Don't forget to star this repo 😉

import * as trpc from '@trpc/server'
import { rule, shield, and, or, not } from 'trpc-shield'

// Rules

const isAuthenticated = rule()(async (ctx, type, path, rawInput) => {
  return ctx.user !== null
})

const isAdmin = rule()(async (ctx, type, path, rawInput) => {
  return ctx.user.role === 'admin'
})

const isEditor = rule()(async (ctx, type, path, rawInput) => {
  return ctx.user.role === 'editor'
})

// Permissions

const permissions = shield({
  query: {
    frontPage: not(isAuthenticated),
    fruits: and(isAuthenticated, or(isAdmin, isEditor)),
    customers: and(isAuthenticated, isAdmin),
  },
  mutation: {
    addFruitToBasket: isAuthenticated,
  },
})

export function createRouter() {
  return trpc.router<Context>().middleware(permissions)
}

WildCard Pattern

const permissions = shield({
  query: {
    "user.*": not(isAuthenticated),
    "*.list": isAuthenticated,
  },
  mutation: {
    "*": isAuthenticated
  }
})

For a fully working example, go here.

Documentation

shield(rules?, options?)

Generates tRPC Middleware layer from your rules.

rules

All rules must be created using the rule function.

Limitations

• All rules must have a distinct name. Usually, you won't have to care about this as all names are by default automatically generated to prevent such problems. In case your function needs additional variables from other parts of the code and is defined as a function, you'll set a specific name to your rule to avoid name generation.

// Normal
const admin = rule()(async (ctx, type, path, rawInput) => true)

// With external data
const admin = (bool) => rule(`name-${bool}`)(async (ctx, type, path, rawInput) => bool)

options

Property	Required	Default	Description
allowExternalErrors	false	false	Toggle catching internal errors.
debug	false	false	Toggle debug mode.
fallbackRule	false	allow	The default rule for every "rule-undefined" field.
fallbackError	false	Error('Not Authorised!')	Error Permission system fallbacks to.

By default shield ensures no internal data is exposed to client if it was not meant to be. Therefore, all thrown errors during execution resolve in Not Authorised! error message if not otherwise specified using error wrapper. This can be turned off by setting allowExternalErrors option to true.

Basic rules

allow, deny are tRPC Shield predefined rules.

allow and deny rules do exactly what their names describe.

Logic Rules

and, or, not, chain, race

and, or and not allow you to nest rules in logic operations.

and rule

and rule allows access only if all sub rules used return true.

chain rule

chain rule allows you to chain the rules, meaning that rules won't be executed all at once, but one by one until one fails or all pass.

The left-most rule is executed first.

or rule

or rule allows access if at least one sub rule returns true and no rule throws an error.

race rule

race rule allows you to chain the rules so that execution stops once one of them returns true.

not

not works as usual not in code works.

You may also add a custom error message as the second parameter not(rule, error).

import { shield, rule, and, or } from 'trpc-shield'

const isAdmin = rule()(async (ctx, type, path, rawInput) => {
  return ctx.user.role === 'admin'
})

const isEditor = rule()(async (ctx, type, path, rawInput) => {
  return ctx.user.role === 'editor'
})

const isOwner = rule()(async (ctx, type, path, rawInput) => {
  return ctx.user.items.some((id) => id === parent.id)
})

const permissions = shield({
  query: {
    users: or(isAdmin, isEditor),
  },
  mutation: {
    createBlogPost: or(isAdmin, and(isOwner, isEditor)),
  },
})

Global Fallback Error

tRPC Shield allows you to set a globally defined fallback error that is used instead of Not Authorised! default response. This might be particularly useful for localization. You can use string or even custom Error to define it.

const permissions = shield(
  {
    query: {
      items: allow,
    },
  },
  {
    fallbackError: 'To je napaka!', // meaning "This is a mistake" in Slovene.
  },
)

const permissions = shield(
  {
    query: {
      items: allow,
    },
  },
  {
    fallbackError: new CustomError('You are something special!'),
  },
)

Whitelisting vs Blacklisting

Whitelisting/Blacklisting is no longer available in versions after 3.x.x, and has been replaced in favor of fallbackRule.

Shield allows you to lock-in access. This way, you can seamlessly develop and publish your work without worrying about exposing your data. To lock in your service simply set fallbackRule to deny like this;

const permissions = shield(
  {
    query: {
      users: allow,
    },
  },
  { fallbackRule: deny },
)