User Authorization with CASL library share between backend and frontend

Question

I am looking at a way to implement authorization in both frontend(React) and backend(Node.js, Koa, GraphQL). I have stumbled across the casl package: https://github.com/stalniy/casl .

Though the backend authorization seems pretty straightforward to me, what I don't get is how can I share my authorization rules from the backend to my frontend. One medium post suggested JWT tokens. How would one go about doing that with a JWT token ?

https://medium.com/dailyjs/casl-and-cancan-permissions-sharing-between-ui-and-api-5f1fa8b4bec

Answer 1

It seems CASL has 2 function to achieve this, packRules and unpackRules.

As per documentation in the backend you can do:

import { packRules } from '@casl/ability/extra';
import jwt from 'jsonwebtoken';
import { defineRulesFor } from '../services/appAbility';

app.post('/session', (req, res) => {
  const token = jwt.sign({
    id: req.user.id,
    rules: packRules(defineRulesFor(req.user))
  }, 'jwt secret', { expiresIn: '1d' });

  res.send({ token });
});

And in the frontend you do:

import { unpackRules } from '@casl/ability/extra'
import jwt from 'jsonwebtoken';
import ability from '../services/appAbility';

export default class LoginComponent {
  login(params) {
    return http.post('/session')
      .then((response) => {
        const token = jwt.decode(response.token);
        ability.update(unpackRules(token.rules))
      });
  }
}

https://stalniy.github.io/casl/v4/en/api/casl-ability-extra