Face Control

Face Control is an opinionated access control middleware for Express. It is heavily inspired by authorized, but also provides a more intelligent way to perform permission checks.

Getting Started

Installation

Installing the module is fairly straightforward:

$ npm install face-control --save

Basics

In this section, I will describe basic ideas behind Face Control by giving an example of space fleet permission hierarchy.

Scope

A scope is a domain that contains various roles. For instance, a spaceship captain's ship:captain role is only valid on his ship, therefore ship is the scope and captain is the role contained in that scope.

In order to minimize the number of database round-trips, Face Control gives you an option to tie a scope to a URL parameter via a hint. For instance, when a fleet scope is requested, and URL contains :shipId parameter, it will automagically see that it can first retrieve the ship scope, then from ship.fleetId extract the fleet scope.

/* https://galactic-federation.net/ship/:shipId */
 
/* Teaches Face Control how to find the ship info */
FaceControl.scope('ship', { hint: 'shipId' }, async req => db.ships.find(req.params.shipId));
 
/* Teaches Face Control how to find fleet info from ship info */
FaceControl.scope('fleet', { hint: 'shipId', deps: 'ship' }, async req => {
 
  /* Since 'ship' is a dependency, it will be stored here */
  const ship = req.$fc_cache$.ship;
 
  /* Find the 'fleet' based on the ship */
  return db.fleets.find(ship.fleetId);
 
});
 

As you can see, hint tells Face Control to use the provided callback when there is a :shipId specified, while deps tells it that it needs to retrieve ship info before trying to find out what fleet it is from.

Of course, you can provide multiple hinted callbacks for the same scope. In that case, Face Control will find the most appropriate callback to use.

/* https://galactic-federation.net/fleet/:fleetId */
 
/* Teaches Face Control how to find the fleet info from :fleetId */
FaceControl.scope('fleet', { hint: 'fleetId' }, ...);

Role

A role signifies a set of actions a person is allowed to perform. Roles can be global or tied to a specific scope. It's magic, isn't it?

 
FaceControl.role('ship:captain', function(entity, role, request) {
 
  /* When the role `captain` is used without scope, it makes no sense */
  if (!entity) { throw new Error('Captain must have a ship!'); }
 
  /* Now, we can check if the person IS a captain */
  if (!request.user.isCaptain) { return false; }
 
  /* Here we can check if the user is the captain of THE ship */
  if (entity.id !== request.user.shipId) { return false; }
 
  /* Welcome, captain! */
  return true;
 
});
 

Action

Action is essentially a set of roles that are allowed to perform a certain action. For instance, self-destruct action should only be executed by ship:captain or fleet:admiral. So, here we go:

FaceControl.action('self-destruct', [ 'ship:captain', 'fleet:admiral' ]);

Imply

Let's say we want fleet:admiral to be able to do anything a ship:captain is able to. Writing both roles in every action makes configuration a tangled mess. Instead, you can just say 'let fleet admiral automatically have ship captain powers'!

FaceControl.imply('fleet:admiral', [ 'ship:captain' ]);

After this, when defining actions you only need to specify ship:captain, and the rest is handled for you.

Middleware

So, after going through all the trouble teaching Face Control all fine details of your permission hierarchy, putting it to use is incredibly simple:

app.use(FaceControl('ship:captain', 'hangar:technician'));

And that's it! Face Control will do the rest.

License

MIT