Add support to JWT Bearer

[marcomontalbano]

What I did

JWT Bearer flow allows a client application to obtain an access token using a JSON Web Token (JWT) assertion.

I added support to the JWT bearer flow by introducing a new createAssertion method:

const assertion = await createAssertion({
  payload: {
    'https://commercelayer.io/claims': {
      owner: {
        type: 'Customer',
        id: '4tepftJsT2'
      },
      custom_claim: {
        customer: {
          first_name: 'John',
          last_name: 'Doe'
        }
      }
    }
  }
})

Once you created the assertion you can get an access token using the urn:ietf:params:oauth:grant-type:jwt-bearer grant type:

import { authenticate } from '@commercelayer/js-auth'

const auth = await authenticate('urn:ietf:params:oauth:grant-type:jwt-bearer', {
  clientId: 'your-client-id',
  clientSecret: 'your-client-secret',
  scope: 'market:code:europe',
  assertion
})

console.log('My access token: ', auth.accessToken)
console.log('Expiration date: ', auth.expires)

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests).
• Make sure to add/update documentation regarding your changes.
• You are NOT deprecating/removing a feature.