Logical-permissions NPM

logical-permissions

This is a generic library that provides support for object-based permissions with logic gates such as AND and OR. You can register any kind of permission types such as roles and flags. The idea with this library is to be an ultra-flexible foundation that can be used by any framework. It's tested on node v4 and above but it's probably compatible with older versions as well.

Getting started

Installation

npm install logical-permissions

Usage

//Simple example for checking user roles

var LogicalPermissions = require("logical-permissions");
var lp = new LogicalPermissions();

var roleCallback = function(role, context) {
  var access = false;
  if(context.hasOwnProperty('user') && context.user.hasOwnProperty('roles')) {
    access = context.user.roles.indexOf(role) > -1;
  }
  return access;
};
lp.addType('role', roleCallback);

var permissions = {
  role: ['editor', 'writer']
};

var user = {
  id: 1,
  roles: ['writer']
};

var access = lp.checkAccess(permissions, {user: user});
console.log('Access granted: ' + access);

The main api method is LogicalPermissions::checkAccess(), which checks the access for a permission tree. A permission tree is a bundle of permissions that apply to a specific action. Let's say for example that you want to restrict access for updating a user. You'd like only users with the role "admin" to be able to update any user, but users should also be able to update their own user data (or at least some of it). With the structure this package provides, these conditions could be expressed elegantly in a permission tree as such:

{
  'OR': {
    'role': 'admin',
    'flag': 'is_author'
  }
}

In this example role and flag are the evaluated permission types. For this example to work you will need to register the permission types 'role' and 'flag' so that the class knows which callbacks are responsible for evaluating the respective permission types. You can do that with LogicalPermissions::addType().

Bypassing permissions

This packages also supports rules for bypassing permissions completely for superusers. In order to use this functionality you need to register a callback with LogicalPermissions::setBypassCallback(). The registered callback will run on every permission check and if it returns true, access will automatically be granted. If you want to make exceptions you can do so by adding 'NO_BYPASS': true to the first level of a permission tree. You can even use permissions as conditions for NO_BYPASS.

Examples:

//Disallow access bypassing
{
  'NO_BYPASS': true,
  'role': 'editor'
}

//Disallow access bypassing only if the user is an admin
{
  'NO_BYPASS': {
    'role': 'admin'
  },
  'role': 'editor'
}

Logic gates

Currently supported logic gates are AND, NAND, OR, NOR, XOR and NOT. You can put logic gates anywhere in a permission tree and nest them to your heart's content. All logic gates support an object or array as their value, except the NOT gate which has special rules. If an object or array of values does not have a logic gate as its key, an OR gate will be assumed.

AND

A logic AND gate returns true if all of its children return true. Otherwise it returns false.

Examples:

//Allow access only if the user is both an editor and a sales person
{
  'role': {
    'AND': ['editor', 'sales']
  }
}

//Allow access if the user is both a sales person and the author of the document
{
  'AND': {
    'role': 'sales',
    'flag': 'is_author'
  }
}

NAND

A logic NAND gate returns true if one or more of its children returns false. Otherwise it returns false.

Examples:

//Allow access by anyone except if the user is both an editor and a sales person
{
  'role': {
    'NAND': ['editor', 'sales']
  }
}

//Allow access by anyone, but not if the user is both a sales person and the author of the document.
{
  'NAND': {
    'role': 'sales',
    'flag': 'is_author'
  }
}

OR

A logic OR gate returns true if one or more of its children returns true. Otherwise it returns false.

Examples:

//Allow access if the user is either an editor or a sales person, or both.
{
  'role': {
    'OR': ['editor', 'sales']
  }
}

//Allow access if the user is either a sales person or the author of the document, or both
{
  'OR': {
    'role': 'sales',
    'flag': 'is_author'
  }
}

Shorthand OR

As previously mentioned, any object or array of values that doesn't have a logic gate as its key is interpreted as belonging to an OR gate.

In other words, this permission tree:

{
  'role': ['editor', 'sales']
}

is interpreted exactly the same way as this permission tree:

{
  'role': {
    'OR': ['editor', 'sales']
  }
}

NOR

A logic NOR gate returns true if all of its children returns false. Otherwise it returns false.

Examples:

//Allow access if the user is neither an editor nor a sales person
{
  'role': {
    'NOR': ['editor', 'sales']
  }
}

//Allow neither sales people nor the author of the document to access it
{
  'NOR': {
    'role': 'sales',
    'flag': 'is_author'
  }
}

XOR

A logic XOR gate returns true if one or more of its children returns true and one or more of its children returns false. Otherwise it returns false. An XOR gate requires a minimum of two elements in its value array or object.

Examples:

//Allow access if the user is either an editor or a sales person, but not both
{
  'role': {
    'XOR': ['editor', 'sales']
  }
}

//Allow either sales people or the author of the document to access it, but not if the user is both a sales person and the author
{
  'XOR': {
    'role': 'sales',
    'flag': 'is_author'
  }
}

NOT

A logic NOT gate returns true if its child returns false, and vice versa. The NOT gate is special in that it supports either a string or an object with a single element as its value.

Examples:

//Allow access for anyone except editors
{
  'role': {
    'NOT': 'editor'
  }
}

//Allow access for anyone except the author of the document
{
  'NOT': {
    'flag': 'is_author'
  }
}

Boolean Permissions

Boolean permissions are a special kind of permission. They can be used for allowing or disallowing access for everyone (except those with bypass access). They are not allowed as descendants to a permission type and they may not contain children. Both true booleans and booleans represented as uppercase strings are supported. Of course a simpler way to allow access to everyone is to not define any permissions at all for that action, but it might be nice sometimes to explicitly allow access for everyone.

Examples:

//Allow access for anyone
[
  true
]

//Using a boolean without an array is also permitted
true

//Example with string representation
[
  'TRUE'
]

//Using a string representation without an array is also permitted
'TRUE'

//Deny access for everyone except those with bypass access
[
  false
]

//Using a boolean without an array is also permitted
false

//Example with string representation
[
  'FALSE'
]

//Using a string representation without an array is also permitted
'FALSE'

//Deny access for everyone including those with bypass access
{
  0: false,
  NO_BYPASS: true
}

API Documentation

addType(name, callback)

Adds a permission type.

Parameters

name: String, The name of the permission type

callback: function, The callback that evaluates the permission type. Upon calling checkAccess() the registered callback will be passed two parameters: a permission string (such as a role) and the context object passed to checkAccess(). The permission will always be a single string even if for example multiple roles are accepted. In that case the callback will be called once for each role that is to be evaluated. The callback should return a boolean which determines whether access should be granted.

removeType(name)

Removes a permission type.

Parameters

name: String, The name of the permission type.

typeExists(name)

Checks whether a permission type is registered.

Parameters

name: String, The name of the permission type.

Returns: Boolean, true if the type is found or false if the type isn't found.

getTypeCallback(name)

Gets the callback for a permission type.

Parameters

name: String, The name of the permission type.

Returns: function, Callback for the permission type.

setTypeCallback(name, callback)

Changes the callback for an existing permission type.

Parameters

name: String, The name of the permission type.

getTypes()

Gets all defined permission types.

Returns: Object, permission types with the structure {name: callback, name2: callback2, ...}. This object is shallow cloned.

setTypes(new_types)

Overwrites all defined permission types.

Parameters

new_types: Object, permission types with the structure {name: callback, name2: callback2, ...}. This object is shallow cloned.

getBypassCallback()

Gets the current bypass access callback.

Returns: function, callback for checking access bypass.

setBypassCallback(callback)

Sets the bypass access callback.

Parameters

callback: function, The callback that evaluates access bypassing. Upon calling checkAccess() the registered bypass callback will be passed one parameter, which is the context object passed to checkAccess(). It should return a boolean which determines whether bypass access should be granted.