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authr

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a flexible, expressive, language-agnostic access-control framework.

how it works

authr is an access-control framework. describing it as a "framework" is intentional because out of the box it is not going to automatically start securing your application. it is extremely agnostic about quite a few things. it represents building blocks that can be orchestrated and put together in order to underpin an access-control system. by being so fundamental, it can fit almost any need when it comes to controlling access to specific resources in a particular system.

vocabulary

the framework itself has similar vocabulary to an ABAC access-control system. the key terms are explained below.

subject

a subject in this framework represents an entity that is capable of performing actions; an actor if you will. in most cases this will represent a "user" or an "admin".

resource

a resource represents an entity which can be acted upon. in a blogging application this might be a "post" or a "comment". those are things which can be acted upon by subjects wanting to "edit" them or "delete" them. it is worth noting that subjects can also be resources — a "user" is something that can act and be acted upon.

a resource has attributes which can be analyzed by authr. for example, a post might have an attribute id which is 333. or, a user might have an attribute email which would be [email protected].

action

an action is a simple, terse description of what action is being attempted. if say a "user" was attempting to fix a typo in their "post", the action might just be edit.

rule

a rule is a statement that composes conditions on resource and actions and specifies whether to allow or deny the attempt if the rule is matched. so, for example if you wanted to "allow" a subject to edit a private post, the JSON representation of the rule might look like this:

{
  "access": "allow",
  "where": {
    "action": "edit",
    "rsrc_type": "post",
    "rsrc_match": [["@type", "=", "private"]]
  }
}

notice the lack of anything that specifies conditions on who is actually performing the action. this is important; more on that in a second.

agnosticism through interfaces

across implementations, authr requires that objects implement certain functionality so that its engine can properly analyze resources against a list of rules that belong to a subject.

once the essential objects in an application have implemented these interfaces, the essential question can finally be asked: can this subject perform this action on this resource?

<?php

use Cloudflare\Authr;

class UserController extends Controller
{
    /** @var \Cloudflare\AuthrInterface */
    private $authr;
    ...

    public function update(Request $req, Response $res, array $args)
    {
        // get the subject
        $subject = $req->getActor();

        // get the resource
        $resource = $this->getUser($args['id']);

        // check permissions!
        if (!$this->authr->can($subject, 'update', $resource)) {
            throw new HTTPException\Forbidden('Permission denied!');
        }

        ...
    }
}

forming the subject

authr is most of the time identifiable as an ABAC framework. it relies on the ability to place certain conditions on the attributes of resources. there is however one key difference: there is no way to specify conditions on the subject in rule statements.

instead, the only way to specify that a specific actor is able to perform an action on a resource is to emit a rule from the returned list of rules that will match the action and allow it to happen. therefore, a subject is only ever known as a list of rules.

type Subject interface {
    GetRules() ([]*Rule, error)
}

and instead of the rules being statically defined somewhere and needing to make the framework worry about where to retrieve the rules from, rules belong to subjects and are only ever retrieved from the subject.

when permissions are checked, the framework will simply call a method available via an interface on the subject to retrieve a list of rules for that specific subject. then, it will iterate through that list until it matches a rule and return a boolean based on whether the rule wanted to allow or deny.

why disallow inspection of attributes on the actor?

by reducing actors to just a list of rules, it condenses all of the logic about what a subject is capable of to a single area and keeps it from being scattered all over an application's codebase.

also, in traditional RBAC access-control systems, the notion of checking if a particular actor is in a certain "role" or checking the actors ID to determine access is incredibly brittle and "ages" a codebase.

by having a single component which is responsible for answering the question of access-control, combined with being forced to clearly express what an actor can do with the authr rules, it leads to an incredible separation of concerns and a much more sustainable codebase.

even if authr is not the access-control you choose, there is a distinct advantage to organizing access-control in your services this way, and authr makes sure that things stay that way.

expressing permissions across service boundaries

because the basic unit of permission in authr is a rule defined in JSON, it is possible to let other services do the access-control checks for their own purposes.

an example of this internally at Cloudflare is in a administrative service. by having this permissions defined in JSON, we can simply transfer all the rules down to the front-end (in JavaScript) and allow the front-end to hide/show certain functionality based on the permission of whoever is logged in.

when you can have the front-end and the back-end of a service seamlessly agreeing with each other on access-control by only updating a single rule, once, it can lead to much easier maintainability.

todo

  • [ ] create integration tests that ensure implementations agree with each other
  • [ ] finish go implementation
  • [ ] add examples of full apps using authr for access-contro
  • [ ] add documentation about the rules format

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