exacl

A rewrite of exacl with ES6 features and bugfix. .This module is an express/connect middleware module for enforcing an Apache Shiro inspired authorization system.

Installation

$ npm install exacl

Basic usage

const express = require('express')
const app = express()
const authorization = require("./my_custom_authorization.js");
 
app.get('/restricted', authorization.authorizer.isPermitted("restricted:view"), (req, res) => {
  // Restricted content
  ...
})

Documentation

Definitions

Permission - a statement that defines access to an explicit activity, behaviour or action.

Principal - usually a website user, assigned permissions to enable access to sets of activities, behaviours, or actions.

Permission Wildcard Expressions

To practically assign sets of permissions to principals, exacl supports a wildcard enabled permission statement syntax that closely follows the syntax used by Apache Shiro. A collection of permissions assigned to a principal are compiled by the system into a regular expression.

• Permission statements are composed of from parts delimited by colons :.
• Wildcard ? and * can be used to match one or more characters within an expression part.
• Examples:

Expression	Description
'system:*'	String - has all permissions for system. Works for a single permission statement only
[ 'system:*', 'activity:create', 'admin:users:roles:get:* ]	Array - has all permissions for system and create permissions for activity and can retrieve all roles of all users

Initialization

Create a new authorizer in for example a file name authorization.js:

var authorizer = require('exacl');
 
module.exports = authorizer;

Options

Setting options at initialization sets the default for that authorizer. The following options are available:

• withPrincipal - A Principal, usually a user, is expected to be represented by an object with a permissions property referring to either a single permission or an array of permissions. Defaults to req.user or req.session.user.
• onDenied - Callback function for when permission is denied. Defaults to setting the res.status to 403.

Setting the default principal

withPrincipal can be specified using an array, a function or an asynchronous function.

// Use any object that has a "permissions" parameter (array)
var user = {
  username    : 'thisismyusername'
  permissions : [ 'account:view', 'payment:view' ]
}
authorizer.options.withPrincipal = user
// OR use a function that returns a valid subject
authorizer.options.withPrincipal = (req, res) => {
  var user = {
    username    : 'thisismyusername'
    permissions : [ 'account:view', 'payment:view' ]
  }
  return user
}
// OR use an asynchronous function that return a promise.
authorizer.options.withPrincipal = async (req, res) => {
  var user = await {
    username    : 'thisismyusername'
    permissions : [ 'account:view', 'payment:view' ]
  }
  return user
}

Setting the default onDenied callback

onDenied must be an express/connect compatible middleware function

authorizer.options.onDenied = (err, res) => {
  res.status(403).send({error: err});
}

Express Middleware

exacl uses a fluent API to generate express middleware for enforcing permissions.

const authorization = require("./authorization.js"); // Where the authorizer was configured previously.
 
app.get('/restricted', authorization.authorizer.isPermitted("restricted:view"), (req, res) => {
  // Restricted content
  ...
})