Linking Zot And Keycloak Via OIDC: A Comprehensive Guide

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Hey guys! Ever found yourself wrestling with Zot and Keycloak, trying to get them to play nice via OIDC? It can be a real head-scratcher when things don't link up as expected, especially when you're staring at a docker login zot.local command that just refuses to cooperate. If you've been banging your head against the wall because the WWW-Authenticate header is MIA in your registry's 401 response, you're in the right place. Let's dive into the nitty-gritty of how to get Zot and Keycloak talking smoothly using OpenID Connect (OIDC). We'll break down the steps, troubleshoot common issues, and get you on the path to seamless authentication. So, grab your favorite caffeinated beverage, and let's get started!

Understanding the Basics: Zot, Keycloak, and OIDC

Before we jump into the configuration, let's make sure we're all on the same page with the key players in this scenario:

  • Zot: Think of Zot as your friendly neighborhood container registry. It's where you store and manage your Docker images, Helm charts, and other OCI artifacts. Zot is designed to be lightweight and efficient, making it a great choice for various deployment environments.
  • Keycloak: Keycloak is an open-source identity and access management solution. It handles user authentication, authorization, and identity federation. In our case, Keycloak will act as the OIDC provider, verifying user identities and issuing access tokens.
  • OIDC (OpenID Connect): OIDC is an authentication layer built on top of OAuth 2.0. It allows clients (like Zot) to verify the identity of users based on the authentication performed by an authorization server (like Keycloak), as well as to obtain basic profile information about the user. OIDC is the glue that allows Zot to trust Keycloak's authentication decisions.

In essence, when you try to docker login zot.local, Zot needs a way to verify who you are. Instead of managing usernames and passwords itself, Zot delegates this responsibility to Keycloak via OIDC. Keycloak checks your credentials and, if they're valid, issues a token that Zot trusts. This setup centralizes authentication, making it more secure and easier to manage.

Step-by-Step Configuration: Linking Zot and Keycloak

Alright, let's get our hands dirty and configure Zot to authenticate against Keycloak using OIDC. Here’s a step-by-step guide to walk you through the process:

1. Keycloak Setup

First, you'll need to set up Keycloak. If you haven't already, download and install Keycloak. Once it's running, follow these steps:

  • Create a Realm: A realm in Keycloak is like a namespace. It allows you to manage a set of users, applications, and roles. Create a new realm specifically for your Zot registry. Give it a meaningful name, like zot-realm.
  • Create a Client: A client in Keycloak represents an application that wants to authenticate users. Create a new client for Zot. Make sure to configure the following settings:
    • Client ID: This is a unique identifier for your Zot client. Choose something descriptive, like zot-registry.
    • Client Protocol: Set this to openid-connect.
    • Access Type: Choose confidential if Zot will be running on a server and can securely store a client secret. Choose public if Zot is running in a less secure environment.
    • Standard Flow Enabled: Turn this on.
    • Valid Redirect URIs: This is a critical setting. Set this to the URL where Keycloak will redirect the user after successful authentication. For Zot, this will typically be something like http://zot.local/v2/auth/callback.
    • Web Origins: Add http://zot.local to the Web Origins.
  • Create a User: Create a user in Keycloak that you'll use to log in to your Zot registry. Assign the user to the zot-realm realm.

2. Zot Configuration

Next, you'll need to configure Zot to use Keycloak for authentication. This typically involves modifying Zot's configuration file. Here's a sample configuration snippet:

auth:
  issuer: <KEYCLOAK_ISSUER_URL>
  realm: zot-realm
  service: zot
  jwks_uri: <KEYCLOAK_JWKS_URI>
  client_id: zot-registry
  client_secret: <YOUR_CLIENT_SECRET>

Replace the placeholders with the actual values from your Keycloak setup:

  • <KEYCLOAK_ISSUER_URL>: This is the URL of your Keycloak instance, including the realm. It should look something like http://localhost:8080/realms/zot-realm.
  • <KEYCLOAK_JWKS_URI>: This is the URL where Zot can retrieve Keycloak's JSON Web Key Set (JWKS). This is used to verify the signature of the tokens issued by Keycloak. It should look something like http://localhost:8080/realms/zot-realm/protocol/openid-connect/certs.
  • <YOUR_CLIENT_SECRET>: This is the client secret you generated when creating the Zot client in Keycloak. Important: Keep this secret safe!

3. Docker Login

With Keycloak and Zot configured, you should now be able to log in to your Zot registry using Docker. Run the following command:

docker login zot.local

Docker will prompt you for your username and password. Enter the credentials of the user you created in Keycloak. If everything is configured correctly, you should be successfully logged in!

Troubleshooting Common Issues

Even with careful configuration, things can sometimes go wrong. Here are some common issues you might encounter and how to troubleshoot them:

1. Missing WWW-Authenticate Header

If you're seeing a 401 response without the WWW-Authenticate header, it usually means that Zot is not properly configured to use OIDC. Double-check the following:

  • Configuration File: Ensure that your Zot configuration file is correctly pointing to your Keycloak instance and that all the required parameters (issuer, JWKS URI, client ID, client secret) are set correctly.
  • Restart Zot: After modifying the configuration file, make sure to restart the Zot service for the changes to take effect.
  • Network Connectivity: Verify that Zot can reach your Keycloak instance. Use ping or curl to check network connectivity.

2. Invalid Redirect URI

If you're getting an error related to an invalid redirect URI, it means that the Valid Redirect URIs setting in your Keycloak client configuration does not match the URL that Keycloak is trying to redirect to. Double-check that the Valid Redirect URIs setting is set to http://zot.local/v2/auth/callback (or the appropriate URL for your setup).

3. Token Verification Errors

If you're seeing errors related to token verification, it usually means that Zot is unable to verify the signature of the tokens issued by Keycloak. This could be due to several reasons:

  • Incorrect JWKS URI: Double-check that the jwks_uri setting in your Zot configuration file is correct.
  • Keycloak Configuration: Ensure that Keycloak is properly configured to issue tokens that are compatible with Zot. Check the token signature algorithm and other token settings in Keycloak.
  • Clock Skew: If the clocks on your Zot and Keycloak servers are not synchronized, it can cause token verification errors. Make sure that both servers have accurate time.

4. CORS Issues

CORS (Cross-Origin Resource Sharing) issues can prevent Zot from communicating with Keycloak. If you're seeing CORS errors in your browser's console, you'll need to configure Keycloak to allow cross-origin requests from Zot.

  • Web Origins: Add http://zot.local to the Web Origins in Keycloak's client configuration.

Docker Compose Example

For those of you using Docker Compose, here’s an example of how you might set up Zot and Keycloak:

version: "3.8"
services:
  keycloak:
    image: quay.io/keycloak/keycloak:latest
    environment:
      KEYCLOAK_ADMIN: admin
      KEYCLOAK_ADMIN_PASSWORD: admin
    ports:
      - "8080:8080"
    volumes:
      - keycloak_data:/opt/keycloak/data

  zot:
    image: ghcr.io/project-zot/zot:latest
    ports:
      - "5000:5000"
    environment:
      ZOT_AUTH_ISSUER: http://localhost:8080/realms/zot-realm
      ZOT_AUTH_REALM: zot-realm
      ZOT_AUTH_SERVICE: zot
      ZOT_AUTH_JWKS_URI: http://localhost:8080/realms/zot-realm/protocol/openid-connect/certs
      ZOT_AUTH_CLIENT_ID: zot-registry
      ZOT_AUTH_CLIENT_SECRET: your-client-secret
    volumes:
      - zot_data:/var/lib/zot
    depends_on:
      - keycloak

volumes:
  keycloak_data:
  zot_data:

Remember to replace the placeholders with your actual values and configure Keycloak as described in the previous steps.

Conclusion

Linking Zot and Keycloak via OIDC might seem daunting at first, but with a clear understanding of the components and careful configuration, you can achieve seamless authentication for your container registry. By following the steps outlined in this guide and troubleshooting common issues, you'll be well on your way to a more secure and manageable development environment. Keep experimenting, keep learning, and don't be afraid to dive into the documentation. You've got this! Happy containerizing, folks!