Understanding `openid-client`: The Complete Guide

The openid-client library is a powerful and flexible tool designed to facilitate secure authentication and authorization using the OpenID Connect protocol. This guide provides an in-depth look at the various APIs available within the openid-client library, complete with examples and a sample application to help you get started.

Getting Started with openid-client

First, install the library via npm:

  npm install openid-client

Creating a Client Instance

Begin by creating a client instance using discovery:

  
    const { Issuer } = require('openid-client');
    
    (async () => {
      const oidcIssuer = await Issuer.discover('https://example.com/.well-known/openid-configuration');
      const client = new oidcIssuer.Client({
        client_id: 'my_client_id',
        client_secret: 'my_client_secret',
        redirect_uris: ['https://myapp.com/cb'],
        response_types: ['code'],
      });
      console.log(client.metadata);
    })();
  

Authorization Code Flow

Using the authorization code flow for secure authentication:

  
    const authorizationUrl = client.authorizationUrl({
      scope: 'openid profile email',
      state: 'someRandomState',
    });

    // Redirect the user to authorizationUrl
  

Callback handling after redirection:

  
    const params = client.callbackParams(req);
    const tokenSet = await client.callback('https://myapp.com/cb', params);
    console.log('id_token:', tokenSet.id_token);
  

Refreshing Tokens

Automatically refresh expired tokens:

  
    const refreshedTokenSet = await client.refresh(tokenSet.refresh_token);
    console.log('New tokens:', refreshedTokenSet);
  

Userinfo Endpoint

Retrieve user information:

  
    const userInfo = await client.userinfo(access_token);
    console.log('User info:', userInfo);
  

Example Application

Putting it all together in an Express.js application:

  
    const express = require('express');
    const { Issuer } = require('openid-client');

    (async () => {
      const app = express();
      const oidcIssuer = await Issuer.discover('https://example.com/.well-known/openid-configuration');
      const client = new oidcIssuer.Client({
        client_id: 'my_client_id',
        client_secret: 'my_client_secret',
        redirect_uris: ['https://myapp.com/cb'],
        response_types: ['code'],
      });

      app.get('/login', (req, res) => {
        const authorizationUrl = client.authorizationUrl({
          scope: 'openid profile email',
          state: 'someRandomState',
        });
        res.redirect(authorizationUrl);
      });

      app.get('/cb', async (req, res) => {
        const params = client.callbackParams(req);
        const tokenSet = await client.callback('https://myapp.com/cb', params);
        const userInfo = await client.userinfo(tokenSet.access_token);
        res.send(`
Welcome, ${userInfo.name}
`);
      });

      app.listen(3000, () => console.log('App started on port 3000'));
    })();
  

This guide covers the essential elements required to implement a secure and robust authentication system using the openid-client library. With this knowledge, you can ensure your application remains secure and user-friendly.

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