Keycloak OIDC: Configure, Integrate for Secure SSO

Unlock robust authentication with OpenID Connect (OIDC) and Keycloak. This comprehensive guide will walk you through the essential steps to configure Keycloak as your OIDC provider, enabling secure single sign-on for your applications. Learn how to set up realms, clients, users, and integrate your services for seamless identity management.

Understanding the Basics: OpenID Connect & Keycloak

Before diving into configuration, it’s crucial to grasp the foundational concepts. OpenID Connect (OIDC) is an authentication layer built on top of the OAuth 2.0 authorization framework. It allows clients to verify the identity of the end-user based on authentication performed by an authorization server, as well as to obtain basic profile information about the end-user in an interoperable and REST-like manner. Essentially, it tells you who the user is, unlike OAuth 2.0 which only tells you what they can do.

Keycloak is an open-source Identity and Access Management (IAM) solution designed to make applications and services secure with minimal effort. It provides features like Single Sign-On (SSO), Identity Brokering, and User Federation. When combined, Keycloak acts as your OIDC Provider, handling all the complex authentication flows, token issuance, and user management, allowing your applications to delegate authentication securely and efficiently.

Keycloak Setup: Realm, Client, and Users

This chapter outlines the practical steps within the Keycloak administration console to prepare it as an OIDC provider.

1. Create a Realm: A realm in Keycloak is a dedicated space for managing users, applications, and roles.
   • Log into your Keycloak admin console.
   • Hover over “Master” in the top-left navigation and click “Add realm”.
   • Give it a descriptive name (e.g., MyApplicationRealm) and click “Create”.
2. Add an OIDC Client: This represents your application that will use Keycloak for authentication.
   • Navigate to your newly created realm.
   • Go to “Clients” in the left-hand menu and click “Create client”.
   • For “Client ID”, use a unique identifier (e.g., my-web-app).
   • Select “openid-connect” as the “Client authentication” type (or “public” if it’s a browser-based app without a backend secret).
   • For “Access Type”, choose confidential for server-side applications (requires client secret) or public for client-side applications (e.g., JavaScript SPAs).
   • Crucially, set the “Valid Redirect URIs”. These are the URLs where Keycloak will redirect the user after successful authentication (e.g., http://localhost:8080/callback or https://your-app.com/auth/callback).
   • Optionally, set “Web Origins” if your client uses AJAX requests from a different origin.
   • Save your changes. If you selected confidential, go to the “Credentials” tab for your client and note down the “Secret”. This will be used by your application to authenticate with Keycloak’s token endpoint.
3. Create a User: Users will be authenticating via Keycloak.
   • In your realm, go to “Users” in the left-hand menu and click “Add user”.
   • Fill in details like “Username” and “Email”.
   • Go to the “Credentials” tab for the user, set a password, confirm it, and toggle “Temporary” off if you want a permanent password. Click “Set Password”.

Integrating Your Application with Keycloak OIDC

With Keycloak configured, the next step is to integrate your application to leverage its OIDC capabilities. The most common and secure flow for web applications is the Authorization Code Flow.

1. Initiate Authentication: When a user needs to log in, your application redirects the user’s browser to Keycloak’s authorization endpoint. This redirect URL will include several critical parameters:
   • client_id: The ID of the client you registered in Keycloak (e.g., my-web-app).
   • redirect_uri: The exact URL on your application where Keycloak will send the authorization code (must match a “Valid Redirect URI” configured in Keycloak).
   • response_type=code: Specifies that you expect an authorization code.
   • scope=openid profile email: Requests access to the user’s basic profile and email. openid is mandatory for OIDC.
   • state: A unique, unguessable value generated by your application to prevent CSRF attacks.
   • nonce: Another unique, unguessable value used to mitigate replay attacks and bind the ID Token to the client, especially important for SPAs.

   Example authorization URL structure: https://your-keycloak-domain/auth/realms/MyApplicationRealm/protocol/openid-connect/auth?client_id=my-web-app&redirect_uri=http://localhost:8080/callback&response_type=code&scope=openid%20profile%20email&state=random_string&nonce=another_random_string

2. Receive Authorization Code: After successful authentication by the user on Keycloak, Keycloak redirects the user back to your redirect_uri, appending the code and state parameters to the URL. Your application must verify the received state parameter against the one it sent.
3. Exchange Code for Tokens: Your application then makes a direct back-channel (server-to-server) POST request to Keycloak’s token endpoint (e.g., https://your-keycloak-domain/auth/realms/MyApplicationRealm/protocol/openid-connect/token). This request will include:
   • grant_type=authorization_code
   • client_id
   • client_secret (if confidential client)
   • code (the authorization code received in the previous step)
   • redirect_uri (must match the one used in step 1)

   Keycloak responds with a JSON payload containing the ID Token (a JWT representing the user’s identity), an Access Token (for accessing protected resources), and optionally a Refresh Token (to obtain new access tokens without re-authenticating the user).

4. Verify ID Token: The ID Token is a JSON Web Token (JWT). Your application should verify its signature using Keycloak’s public keys (available at its JWKS endpoint), check the issuer, audience, expiration, and nonce claims to ensure its authenticity and integrity. Once validated, you can extract user information from the ID Token’s claims.

Many programming languages and frameworks offer OIDC client libraries that simplify these steps significantly, abstracting away the low-level HTTP requests and token validation.

You’ve successfully navigated the process of setting up OpenID Connect with Keycloak, from understanding core concepts to configuring realms, clients, and integrating your application. This powerful combination provides a robust, scalable, and secure authentication layer, freeing developers to focus on core application logic. Embrace Keycloak’s OIDC capabilities to streamline identity management and enhance security for your digital ecosystem.