Access Mate

[Attribute-based access control][1] inspired by [xacml][2].

Benefits

Using this model, one can implement virtually any kind of access control; role
based access control, multi-level access control, identity based access
control, etc.

Glossary

- resource: The data that wants to be accessed.
- target: Name of the resource.
- action: What the request wants to do with the resource.
- subject: In most cases this is essentially the authenticated user.
- environment: Data which is not specific to the resource or subject, e.g.,
global settings/configurations.
- effect: If the rule passes, what effect it will have (either deny or allow).
- policy: A policy is the smallest unit of access control. It represents a
single rule. A policy reaches a decision based on the context it is given,
which is the action, resource, subject,
- policy set: A policy set is a list of policies.
- strategy: A strategy decides how to use policies. Mainly, these define
how actions behave, and pass the context over to the policies.

Conditions

Conditions are generated using the o-is module. See [documentation][3] for
details.

API

$3

The policy class is an immutable builder. Methods returning a policy will
return a new instance with the same properties as the previous policy with some
additions done by the method call. For example, if you have a policy with an
action of "update" and decide to call target('user'), this will return a new
policy with an action of "update" and a target of "user" instead of mutating
the current existing one.

#### decision(context)
Returns true if the decision was made to allow access, false if denied,
undefined if unable to reach decision (meaning the condition didn't apply).

#### target(value)
Returns a new policy with the specified targets. Accepts multiple string values
or an array of values.

#### action(value)
Returns a new policy with the specified action. Accepts multiple string values
or an array of values.

#### effect(value)
Returns a new policy with the specified effect. Valid effects are "allow" and
"deny".

#### fields(...values)
Returns a new policy which will only apply to certain fields. This means that
if the policy denies access, it will add the specified fields to the omit
array in the result instead of causing the entire record to fail authorization.

#### condition(value)
Optionally accepts a value which will be "set" as the policie's condition.
If no value is given this will instead return an o-is instance, allowing
construction of the condition immediately.

Example when specifying the condition value:
``javascript
const isAdmin = oIs().true('isAdmin')

// You can define your conditions first and use them on policies later.
const policy = AccessMate.policy()
.condition(isAdmin)
.target('comment')
.effect('allow')
.action('update')
`

Example when not specifying the condition (results in the same thing as the
previous example):
`javascript
const policy = AccessMate.policy()
.condition()
.true('isAdmin')
.end()
.target('comment')
.effect('allow')
.action('update')
`

#### deny()
Concatenates the current policy to the policy set and returns a new policy with
a deny effect.

#### allow()
Concatenates the current policy to the policy set and returns a new policy with
an allow effect.

#### end()
Concatenates the policy to the policy set and returns the policy set.




$3


Much like the Policy, the PolicySet class is immutable. All calls
return a new policy set instead of mutating itself.

#### concat(value)
Concatenates policy sets together.

#### allow()
Returns a new policy with an "allow" effect.

#### deny()
Returns a new policy with a "deny" effect.

#### toJSON()
Returns a serializable representation of the policy set.

#### static fromJSON(json)
Takes the serializable representation and returns a policy set.

#### authorize(context)
Returns an object containing two properties: authorize and omit. If
authorize is true, the user has access to the resource. omit is a list of
fields that the user does not have access to.

The context object must contain an action (string), target (string),
environment (object), resource (object), and subject (object) property.




$3


Strategies determine how actions behave. Policy sets only use actions to
determine if a policy should be applied or not, strategies define additional
behaviour on top of this. All strategies require a policy set and an options
object. The options object usually requires at least resource, subject, and
environment.

#### simple(policySet, options)
A very basic strategy which simply returns the result of the policy set. There
is no special behaviour for this strategy.

#### crud(policySet, options)
The CRUD strategy is identical to the simple strategy except it defines
special behaviour for the updates. For update actions, you will need to pass in
an additional property previousResource which is the resource that was last
updated. There are 3 different kind of update actions which your policies can
use:
- update-into: This action is only applied on the resource which is to be
updated.
- update-from: This action is only applied on the previous revision of the
resource.
- update: This is just a combination of update-into and update-from.

$3


BREAD stands for "browse", "read", "edit", "add", "delete". "Edit" has the
"edit-from" and "edit-into" similar to the "update" action in the CRUD
strategy.

Browse represents a request to list multiple records. For this action, the
strategy requires a resources property instead of resource. This
resources object is then used to return an array of authorization results
instead of the usual single result.




Full Example


`javascript
const AccessMate = require('access-mate')
const oIs = require('o-is')

// conditions can be re-used.
const isOwner = oIs().propsEqual('subject.id', 'resource.owner')

const policySet = AcessMate.policySet()
.deny()
.target('todo_item')
.action('create')
.condition()
.false('subject.premium_account')
.gt('subject.total_items', 50)
.end()
.allow()
.target('todo_item')
.action('create', 'update', 'delete', 'read')
.condition(isOwner)

// Rules can be composed together.
const policy = AccessMate.policy()
.allow()
.target('todo_item')
.action('read')
.condition()
.propsEqual('subject.id', 'resource.collaborators')
.end()

const fullPolicySet = policySet.concat(rule)

const decision = AccessMate.strategies.simple(fullPolicySet, {
environment: {
someGlobalConfigurations: {}
},
resource: {
owner: 'foobar',
value: 'example todo item',
collaborators: []
},
action: 'create',
target: 'todo_item'
subject: {
id: 'foobar'
}
})

`

This access control module can be serialized/deserialized. The above example
would look like the following when converted to JSON:
`json
[
{
"effect": "deny",
"target": "todo_item",
"action": ["create"],
"condition": [
{ "type": "false", "key": "subject.premium_account" },
{ "type": "gt", "key": "subject.total_items", "value": 50 }
]
},
{
"effect": "allow",
"target": "todo_item",
"action": ["create", "update", "delete", "read"],
"condition": [
{ "type": "propsEqual", "keys": ["subject.id", "resource.collaborator"] }
]
},
{
"effect": "allow",
"target": "todo_item",
"action": ["read"],
"condition": [
{ "type": "propsEqual", "keys": ["subject.id", "resource.collaborator"] }
]
}
]

`




Debugging


This module uses the debug package for managing debug logs. Simply set your
DEBUG` environment variable to include this package's name to enable it.

[1]: https://en.wikipedia.org/wiki/Attribute-based_access_control
[2]: http://docs.oasis-open.org/xacml/3.0/errata01/os/xacml-3.0-core-spec-errata01-os-complete.html
[3]: https://github.com/AGhost-7/o-is/tree/master/packages/o-is