Group/rule-based authorization approach in node.js and express.js

Question

What are good strategies for role-based authorization in express.js? Especially with express-resource?

With Express-resource there are no handlers, so I think there are three options:

1. Use a middleware
2. Pass the authorization function to the resource and check each resource request separately
3. Check authorization with every request right after authentication

Are there any other solutions?

Group/Role-based authorization is a pretty antique approach. Are there newer methods of access control? If not, how can role-based authorization be applied to node.js? Where to store group-rule relationships (with NoSQL/CouchDB/Redis)?

As an example, the structure:

/
  /forums
    /forums/threads

Each resource with index, new, create, show, edit update and destroy. Some people can edit/delete etc. threads and forums, some people shouldn't.

Answer 1

I would say that it's hard to solve this in a clean manner using express-resource, since it doesn't allow for route-specific middleware (at least not in a clean way).

I would opt for a similar layout as an express-resource module, but route it with plain old express. Something like this:

// Resource
var forum = {
  index: // ...
  show: // ...
  create: // ...
  update: // ...
  destroy: // ...
};

// Middleware
var requireRole = function(role) {
  return function(req, res, next) {
    if('user' in req.session && req.session.user.role === role)
      next();
    else
      res.send(403);
  }
};

// Routing
app.get('/forums', forum.index);
app.get('/forums/:id', forum.show);
app.post('/forums', requireRole('moderator'), forum.create); // Only moderators can create forums
app.delete('/forums/:id', requireRole('admin'), forum.destroy); // Only admins can delete forums

UPDATE: There have been ongoing discussions regarding route-specific middleware in express-resource, e.g. here. The prevailing view seems to be to have an array per action, e.g.:

var forums = {
  index: [ requireRole('foo'), function(req, res, next) { ... } ]
};

You could take a look through the pull requests and see if there is anything you could use. I totally understand it, of course, if you don't feel comfortable with that. I'm pretty sure we will see something like this in express-resource in the future.

The only other solution I can think of is along the lines of Jan Jongboom's answer, which would be to mount the resources with express-resource, but have middleware attached "outside" of that, something like:

app.delete('*', requireRole('admin')); // Only admins are allowed to delete anything
app.put('/forums/*', requireRole('moderator')); // Only moderators are allowed to update forums

But I regret that this leaks URLs all over the place.

Answer 2

I have been researching the same question and have come across a few good modules. I have been focusing on the node-acl package that can be found here. https://github.com/optimalbits/node_acl.

This package seems to have implemented the ACL pattern in a very understandable way and has provided ways to easily integrate it into your node/express application.

Firstly, you'll want to define your resources, roles, and permissions.

For example, the resources can be:

/
  /forums
    /forums/threads

The roles can be

public
admin
user
   john
   jane

In this example, the roles john and jane can map to actual user accounts, but they will inherit all the permissions of the user role.

The permissions on the resources

• create
• show
• update
• destroy

Or your standard CRUD operations.

Now that those have been defined, we can take a look at how it would look to set up the acl using node-acl. These notes are derived from the documentation

import the package

var acl = require('acl');

Set up your backend. My app is using mongodb, but the node-acl package does support other storage mechanisms

acl = new acl(new acl.mongodbBackend(dbInstance, prefix));

My app is using mongoose so dbInstance would be replaced with mongoose.connection.db

Now lets add our roles to the ACL. In node-acl, roles are created by giving them permissions. Its like killing two birds with one stone (no birds are actually harmed)

acl.allow('admin', ['/', '/forum', '/forum/threads'], '*');
acl.allow('public', ['/', '/forum', '/forum/threads'], 'show');
acl.allow('user', ['/', '/forum', '/forum/threads'], ['create', 'show']);

Lets assume a new resource is created by john, we will add a new record that allows john to also update and delete that resource.

acl.allow('john', ['/forum/threads/abc123'], ['update', 'delete']);

My application is also using express, so I will use the routing middleware approach to check routes. In my routing configuration, I would add the line

In most express configurations, this looks like for the pos

app.post('/', acl.middleware(), function(req, res, next) {...});
app.post('/forums', acl.middleware(), function(req, res, next) {...});
app.post('/forums/:forumId', acl.middleware(), function(req, res, next) {...});
app.post('/forums/threads', acl.middleware(), function(req, res, next) {...});
app.post('/forums/threads/:threadId', acl.middleware(), function(req, res, next) {...});

When no parameters are passed, this will check if the role defined in req.userId is allowed to execute the http method on the resource identified but the route.

In this example the http method is post, but it will do the same thing for each http idenitified in your configuration.

This raises the question, about the permissions defined earlier. To answer those questions, we would have to change the permissions from

• create
• show
• update
• destroy

To the conventional

• post
• get
• put
• delete

Although this example shows everything hardcoded, the better practice is to have a management interface for your permissions so they can be created, read, updated, and deleted dynamically without having to modify your code.

I like the node-acl plugins approach as it allows for very fine grained permission-role assignments using a very straight forward and flexible api. There is a lot more in their documentation, my example shows were I am with the package.

Hopefully this helps.

Answer 3

Connect-roles is quite good, simple and the documentation is also very clear.

var user = roles;

app.get('/profile/:id', user.can('edit profile'), function (req, res) {
  req.render('profile-edit', { id: req.params.id }); 
})
app.get('/admin', user.is('admin'), function (req, res) {
  res.render('admin');
}

Answer 4

In express you can add a handler that hooks into every operator (http://expressjs.com/guide.html#passing-route control) where you can do precondition validation. Here you can retrieve the role for the user and restrict access based on the HTTP verb (PUT, DELETE, etc.) or the URL (param('op') is 'edit' or so).

app.all('/user/:id/:op?', function(req, res, next){
  req.user = users[req.params.id];
  if (req.user) {
    next();
  } else {
    next(new Error('cannot find user ' + req.params.id));
  }
});

Answer 5

I wrote a module as non-explicit routing middleware. Works well with express-routes.

Gandalf on GitHub

Answer 6

You can try Casbin: https://casbin.org/, it has a Node.js version. It also has a Express.js middleware called express-authz: https://casbin.org/docs/en/middlewares