Add custom fields to a JWT Access Token

Learn how to add custom attributes to a JWT Access Token using Authgear

JWTs (JSON Web Tokens) are a common method for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. With Authgear, it is straightforward to add custom fields to your JWT access tokens.

This how-to guide will walk you through the process of adding custom fields such as User Profiles attributes to a JWT access token payload using Authgear and Javascript Hooks.

Here's an example of the fields in the JWT Access Tokens by default and an explanation of their values.

You can also add custom attributes to User Profiles on the Authegear Portal.

Prerequisites

• An Authgear account: You need an Authgear account to follow this guide. If you don't have one, you can create it for free on the Authgear website.

• A Registered App: You need a registered application (client) in Authgear.

Enable Access Token for your App

Make sure the option Issue JWT as access token is enabled in your Application settings in the Portal.

1. Log into your Authgear account.

2. Navigate to the Applications tab and choose the existing App.

3. On the App Configuration dashboard, locate the "Access token" section.

4. Make the toggle Issue JWT as access token switch on.

Create a new Event Hook

With the use of Hooks, Authgear provides flexibility for adding custom logic to your authentication pipeline. You can create a Hook which is triggered any of these Events about to occur. For example, oidc.jwt.pre_create the event happens just before issuing the JWT access token and it can be used to put extra information into the token.

1. Navigate to your Authgear Dashboard's Advanced->Hooks section.

2. Add a new Blocking Event.

3. Choose the Block Hook Type as the TypeScript and set the Event option to JWT access token pre-create. You will write a new Typescript function from scratch.

1. Click on Edit Script under the Config option.

2. Copy and paste the following into the editor:

import { EventOIDCJWTPreCreate, HookResponse } from "https://deno.land/x/authgear_deno_hook@v1.0.0/mod.ts";

export default async function(e: EventOIDCJWTPreCreate): Promise<HookResponse> {
  return {
    mutations:{
      jwt: {
        payload:{
          ...e.payload.jwt.payload,
          standard_attributes: e.payload.user.standard_attributes,
          custom_attributes: e.payload.user.custom_attributes
        }
      }
    },
    is_allowed: true
  };
}

1. Click on Finish Editing.

2. Back to the Hooks page from the navigation bar and click on the Save button at the top of the page.

In the above code, we are importing the necessary modules such as HookResponse and EventOIDCJWTPreCreate which are types from the Authgear Deno hook Typescript library. We modify the JWT payload by adding Standard Attributes(e.payload.user.standard_attributes) and Custom Attributes(e.payload.user.custom_attributes) of the user.

Verify the Custom Field in a JWT token

There are two ways to test it:

• You can do this by decoding the JWT token on your application server side using a JWT decoder and inspecting the payload.
• If you created the application type OIDC Client Application, you need to follow the steps below. Expand it to see instructions.

Verify the custom field in the JWT Token with OIDC Client Application

This part explains how to retrieve an access token using OpenID App Endpoints and check if newly added custom attributes are in place in the JWT Access token.

Prerequisites

• Make sure that you have a registered app type of OIDC Client Application in Authgear Portal.

Step 1: Obtain the necessary parameters

Open your OpenID Auth App configuration, and find Client ID, Client Secret, and check Authorization, and Token endpoints. You will use them in the next steps.

Step 2: Construct the authorization endpoint URL

The URL for this endpoint is usually provided by the authorization server and includes parameters specifying the requested scope, client_id, and response_type. Here's an example URL for the authorization endpoint:

https://<YOUR_AUTHGEAR_ENDPOINT>/oauth2/authorize?client_id={YOUR_CLIENT_ID}&response_type=code&scope=openid

Replace <YOUR_AUTHGEAR_ENDPOINT> with your Authgear server's domain, YOUR_CLIENT_ID with your application's Client ID from OpenID App.

Step 3: Redirect the user to the authorization endpoint

Next, you need to redirect the user to the authorization endpoint. You can just put the URL in your browser and log in with a user credential you are interested to retrieve an access token for. After successful authentication and consent, the Authgear will redirect the user back to your specified redirect URI, including an authorization code as a query parameter. You will need the code in the next step

Step 4: Obtain an access token

You need to make a request to the OpenID App's Token endpoint to exchange the authorization code we retrieved in the previous step for an access token.

• The token endpoint URL is usually something like https://<YOUR_AUTHGEAR_ENDPOINT>/oauth2/token.

• Include parameters such as grant_type=authorization_code, code=AUTHORIZATION_CODE, client_id=YOUR_CLIENT_ID, client_secret=YOUR_CLIENT_SECRET, and redirect_uri=YOUR_REDIRECT_URI.

• Make a POST request to the token endpoint to obtain the access token.

curl --request POST \
  --url 'https://<YOUR_AUTHGEAR_ENDPOINT>/oauth2/token' \
  --header 'content-type: application/x-www-form-urlencoded' \
  --data grant_type=authorization_code \
  --data code={YOUR_AUTHORIZATION_CODE} \
  --data redirect_uri={YOUR_REDIRECT_URI} \
  --data 'client_id={YOUR_CLIENT_ID}' \
  --data client_secret={YOUR_CLIENT_SECRET} \
  --data scope=openid

Step 5: Verify custom attributes in the access token

Finally, we can debug the access token using the JWT Debugger tool to see if the custom field and value we added previously are there inside the JWT payload.

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