Today, we're going to pop the hood on Keycloak and get our hands dirty with custom mappings, extensions, and integrations. Buckle up, because this ride is about to get wild!

TL;DR

We're diving deep into Keycloak customization, covering:

  • Custom user attribute mappings
  • Building Keycloak extensions (SPIs)
  • Implementing custom authentication flows
  • Integrating with external systems

If you're ready to turn Keycloak into your personal auth playground, read on!

Custom User Attribute Mappings: Because One Size Doesn't Fit All

Let's face it, the out-of-the-box user attributes in Keycloak are about as exciting as vanilla ice cream. But fear not! We can spice things up with custom attribute mappings.

Adding Custom Attributes

First, let's add a custom attribute to our users. In the Keycloak admin console:

  1. Navigate to Users > Attributes
  2. Add a new attribute, let's say "favoriteProgLanguage"

Now, let's map this to a claim in the JWT token. Head over to Clients > [Your Client] > Client Scopes > Dedicated scope > Add mapper > By Configuration > User Attribute.

Fill in the details:

  • Name: Favorite Programming Language
  • User Attribute: favoriteProgLanguage
  • Token Claim Name: fav_lang

Voila! Now when a user logs in, their JWT will include their favorite programming language. Because why not?

Custom Protocol Mapper

But wait, there's more! What if we want to do some fancy processing on our attributes before they hit the token? Enter custom protocol mappers.

Let's create a mapper that converts our favorite language to uppercase (because shouting about our love for Python is totally normal).


public class UppercaseLanguageMapper extends AbstractOIDCProtocolMapper implements OIDCAccessTokenMapper, OIDCIDTokenMapper, UserInfoTokenMapper {

    public static final String PROVIDER_ID = "uppercase-language-mapper";

    @Override
    public String getDisplayCategory() {
        return TOKEN_MAPPER_CATEGORY;
    }

    @Override
    public String getDisplayType() {
        return "Uppercase Language Mapper";
    }

    @Override
    public String getId() {
        return PROVIDER_ID;
    }

    @Override
    protected void setClaim(IDToken token, ProtocolMapperModel mappingModel, UserSessionModel userSession) {
        UserModel user = userSession.getUser();
        String favLang = user.getFirstAttribute("favoriteProgLanguage");
        if (favLang != null) {
            token.getOtherClaims().put("FAV_LANG", favLang.toUpperCase());
        }
    }
}

Now that's what I call a custom mapping! Your favorite language will be screamed from the rooftops (or at least from your JWT).

Keycloak Extensions: Because Sometimes You Need to Break the Rules

Keycloak's extensibility is like a playground for auth nerds. Let's build a simple SPI (Service Provider Interface) that adds a custom action to the authentication flow.

Creating a Custom Authenticator

Imagine we want to add an authenticator that checks if the user's password contains their username (a security no-no). Here's a simplified version:


public class UsernamePasswordValidator implements Authenticator {

    @Override
    public void authenticate(AuthenticationFlowContext context) {
        UserModel user = context.getUser();
        CredentialInput input = context.getHttpRequest().getDecodedFormParameters().getFirst(CredentialForm.PASSWORD);
        
        if (input.getValue().contains(user.getUsername())) {
            context.failureChallenge(AuthenticationFlowError.INVALID_CREDENTIALS, 
                context.form().setError("passwordContainsUsername").createErrorPage());
            return;
        }
        
        context.success();
    }

    // ... other required methods
}

Now, you'll need to register this authenticator with Keycloak and add it to your authentication flow. Your users will thank you later (or curse you now, it's a toss-up).

Custom Authentication Logic: Because Sometimes You Need to Be a Special Snowflake

Let's say your company has a super-secret authentication method involving a magic 8-ball and a cup of coffee. Fear not, Keycloak's got your back!

Implementing a Custom Authentication Flow

Here's a taste of what a custom authentication flow might look like:


public class CoffeeAuthenticator implements Authenticator {

    @Override
    public void authenticate(AuthenticationFlowContext context) {
        if (isCoffeeBrewed() && magicBallSaysYes()) {
            context.success();
        } else {
            context.failureChallenge(AuthenticationFlowError.INVALID_CREDENTIALS, 
                context.form().setError("needMoreCoffee").createErrorPage());
        }
    }

    private boolean isCoffeeBrewed() {
        // Implement your coffee-checking logic here
        return true;  // Optimists, unite!
    }

    private boolean magicBallSaysYes() {
        // Consult the magic 8-ball
        return Math.random() > 0.5;  // 50/50 chance, seems legit
    }

    // ... other required methods
}

Remember, with great power comes great responsibility. Use this knowledge wisely, or you might end up with an authentication system that only works before the coffee runs out.

Integrating with External Systems: Playing Nice with Others

Keycloak doesn't have to be a lone wolf. Let's see how we can make it play nice with external systems.

Custom User Storage Provider

Imagine you have user data stored in a legacy system that uses punch cards (because why not?). Here's a simplified example of how you might integrate that with Keycloak:


public class PunchCardUserStorageProvider implements UserStorageProvider, UserLookupProvider, CredentialInputValidator {

    private PunchCardSystem punchCardSystem;

    @Override
    public UserModel getUserByUsername(String username, RealmModel realm) {
        PunchCardUser punchCardUser = punchCardSystem.findUserByHoles(username);
        if (punchCardUser != null) {
            return new UserAdapter(session, realm, model, punchCardUser);
        }
        return null;
    }

    @Override
    public boolean isValid(RealmModel realm, UserModel user, CredentialInput input) {
        if (!supportsCredentialType(input.getType())) return false;

        return punchCardSystem.validateCard(user.getUsername(), input.getChallengeResponse());
    }

    // ... other required methods
}

Now your vintage punch card system can authenticate users in Keycloak. Welcome to the 21st century... sort of.

The Bottom Line: Keycloak is Your Oyster

We've only scratched the surface of what's possible with Keycloak customization. From tweaking user attributes to building full-blown authentication providers, Keycloak provides a robust platform for tailoring your auth system to your heart's content.

Remember, with great power comes great responsibility (and potentially great headaches). Test thoroughly, document religiously, and may the auth gods be ever in your favor.

Key Takeaways:

  • Custom attribute mappings let you add flair to your tokens
  • SPIs open up a world of extensibility
  • Custom authentication flows allow for unique (and potentially caffeinated) auth logic
  • External system integration is possible, even for the most legacy of systems

Now go forth and customize! And remember, if anyone asks why you spent a week implementing a coffee-based authentication system, just tell them it's for "enhanced security". They'll totally buy it.

"The only way to do great work is to love what you do." - Steve Jobs

(He probably wasn't talking about Keycloak customization, but we can pretend.)

Happy coding, and may your tokens always be valid and your coffee always be strong!