Access Decision Manager - Express.

Determines whether or not an entity is entitled to perform a specific action, for example, request a particular URI or modify a specific object. It relies on Voters, all voters are called each time you use isGranted() method.

The Access Decision Manager takes the responses from all voters and makes the final verdict (to allow or deny access to the resource) according to the strategy defined in the application.

It recognizes several strategies:

affirmative (default)

grant access as soon as there is one voter granting access;

unanimous

only grant access if none of the voters has denied access;

[custom]

(any strategy can be defined and passed as an argument)

Implementing Voters

Voters are to determine access rights The use of Voters to verify permissions is based on this model. Voters are called to grant access to a resource or an action.

Adding a Custom Voter.

To create a Voter, use the Voter interface:

export interface Voter {
 supports: (attribute: any, subject: any, context: any) => boolean;
 voteOnAttribute: (
   attribute: any,
   subject: any,
   user: any,
   context: any,
 ) => boolean | Promise<boolean>;
}

Here's a detailed description of the two abstract methods:

supports(attribute, subject, context) When isGranted() is called, the first argument is passed here as attribute (e.g. ROLE_USER, edit) and the second argument (if any) is passed as subject (e.g. null, a Post object). Your job is to determine if your voter should vote on the attribute/subject combination. if you return true, voteOnAttribute() will be called. Otherwise, your voter is done: some other voters should process this. The third argument, context is to help you to determine access rights, the access decision manager takes this argument when is created

voteOnAttribue(attribute, subject, user, context) If you return true from supports, then this method is called. Your job is simple: return true to allow access and false to deny access. The user and context properties (if any) can be useful.

For example, the following voter checks attributes related to an admin:

Suppose you have a Private object, and you need to decide whether or not the current user can edit the resource. The only users that can get that resource are the ones who are admins; also, you know that the users who are admins have a roles property, which includes admin. So, it would be best if you created a new voter that validates what actions supports in this case GET_PRIVATE. And that the voteOnAttribute validates that the user is an admin.

This voter can be named admin.voter.ts since it is the one which determines access for admin users.

const supportedAttributes = [
 "GET_PRIVATE"
];

const adminVoter = {
 supports(attribute): boolean {
   return supportedAttributes.includes(attribute);
 },
 voteOnAttribute(attribute, subject, user): boolean {
   // Do the logic here to validate determine if has permissions.
   return (
     user &&
     user.roles &&
     user.roles.includes('admin')
   );
 }
}

export default adminVoter;

Then we can have a public resource that can be view for everyone, in this case we need specified the attributes and the logic to validate, since we know this is public we are returning a true.

const supportedAttributes = [
 'GET_PUBLIC'
];

const publicVoter = {
 supports(attribute): boolean {
   return supportedAttributes.includes(attribute);
 },
 voteOnAttribute(attribute, subject, user): boolean {
   // Do the logic here to validate determine if has permissions.
   return true;
 }
}

export default publicVoter;

Then let's add our voters to our express application, here we are assuming that we have the data of our user in req.user

import AccessDecisionManagerProvider, { Voter } from '@wizeline/access-decision-manager-express';
import express from 'express'
import publicVoter from '../path/to/voters';
import privateVoter from '../path/to/voters';

const voters: Voter[] = [
    publicVoter,
    privateVoter
];


const app: express.Application = express();


app.use(AccessDecisionManagerProvider((req) => req.user, voters({})));

Now add the middleware in the routers with their attributes

import { isGrantedMiddleware } from '@wizeline/access-decision-manager-express';

///....

app.get('/publicResource',
  isGrantedMiddleware('GET_PUBLIC'),
  /// ...someController.getAll,
);


app.get('/privateResource',
  isGrantedMiddleware('GET_PRIVATE'),
  /// ...someAnotherController.getAll,
);