1. Getting Started
2. What you will need
3. Solution
4. Run Keycloak on Docker
5. Writing the Application
6. Running the Application
7. Generate a Micronaut Application Native Executable with GraalVM
- 7.1. Native executable generation
8. Next steps
9. Help with the Micronaut Framework

Secure a Micronaut application with Keycloak

Learn how to create a Micronaut application and secure it with an Authorization Server provided by Keycloak.

Authors: Sergio del Amo

Micronaut Version: 3.9.2

1. Getting Started

In this guide, we will create a Micronaut application written in Java.

2. What you will need

To complete this guide, you will need the following:

Some time on your hands
A decent text editor or IDE
JDK 1.8 or greater installed with JAVA_HOME configured appropriately

3. Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

Download and unzip the source

4. Run Keycloak on Docker

Follow the tutorial Get started with Keycloak on Docker.

Replace the client creation in the tutorial with the steps illustrated following screenshots.

Set http://localhost:8081/oauth/callback/keycloak as Valid redirect URIs and http://localhost:8081/logout as Valid post logout redirect URIs.

5. Writing the Application

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app example.micronaut.micronautguide \
    --features=graalvm,views-thymeleaf,security-jwt,security-oauth2 \
    --build=maven
    --lang=java

If you don’t specify the --build argument, Gradle is used as the build tool.
If you don’t specify the --lang argument, Java is used as the language.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

If you use Micronaut Launch, select Micronaut Application as application type and add graalvm, views-thymeleaf, security-jwt, and security-oauth2 features.

If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features and apply those changes to your application.

Setup IntelliJ IDEA to develop Micronaut Applications.

5.1. Dev default environment

Modify Application to use dev as a default environment.

src/main/java/example/micronaut/Application.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.context.ApplicationContextBuilder;
import io.micronaut.context.ApplicationContextConfigurer;
import io.micronaut.context.annotation.ContextConfigurer;
import io.micronaut.runtime.Micronaut;

public class Application {

    @ContextConfigurer
    public static class Configurer implements ApplicationContextConfigurer {
        @Override
        public void configure(@NonNull ApplicationContextBuilder builder) {
            builder.defaultEnvironments("dev");
        }
    }
    public static void main(String[] args) {
        Micronaut.run(Application.class, args);
    }
}

5.2. Start in Port 8081

Create src/main/resources/application-dev.yml. The Micronaut framework applies this configuration file only for the dev environment.

Configure the application to start in port 8081:

src/main/resources/application-dev.yml

micronaut:
  server:
    port: 8081

5.3. Views

Although the Micronaut framework is primarily designed around message encoding / decoding, there are occasions where it is convenient to render a view on the server side.

To use Thymeleaf Java template engine to render views in a Micronaut application add the following dependency on your classpath.

pom.xml

<dependency>
    <groupId>io.micronaut.views</groupId>
    <artifactId>micronaut-views-thymeleaf</artifactId>
    <scope>compile</scope>
</dependency>

5.4. OAuth 2.0

To use OAuth 2.0 integration, add the following dependency:

pom.xml

<dependency>
    <groupId>io.micronaut.security</groupId>
    <artifactId>micronaut-security-oauth2</artifactId>
    <scope>compile</scope>
</dependency>

Also add JWT Micronaut JWT support dependencies:

pom.xml

<dependency>
    <groupId>io.micronaut.security</groupId>
    <artifactId>micronaut-security-jwt</artifactId>
    <scope>compile</scope>
</dependency>

5.5. OAuth 2.0 Configuration

Add the following OAuth2 Configuration:

src/main/resources/application-dev.yml

micronaut:
  security:
    authentication: idtoken (1)
    oauth2:
      clients:
        keycloak: (2)
          client-secret: '${OAUTH_CLIENT_SECRET:secret}' (3)
          client-id: '${OAUTH_CLIENT_ID:myclient}' (4)
          openid:
            issuer: '${OIDC_ISSUER_DOMAIN:`http://localhost:8080`}/realms/${KEYCLOAK_REALM:myrealm}/' (5)
    endpoints:
      logout:
        get-allowed: true (6)

1	Set `micronaut.security.authentication` as `idtoken`. The `idtoken` provided by Keycloak when the OAuth 2.0 Authorization code flow ends will be saved in a cookie. The id token is a signed JWT. For every request, the Micronaut framework extracts the JWT from the Cookie and validates the JWT signature with the remote Json Web Key Set exposed by Keycloak. JWKS is exposed by the `jws-uri` entry of Keycloak `.well-known/openid-configuration`.
2	The provider identifier should match the last part of the URL you entered as a redirect URL `/oauth/callback/keycloak`
3	Client Secret. See previous screenshot.
4	Client ID. See previous screenshot.
5	`issuer` URL. It allows the Micronaut framework to discover the configuration of the OpenID Connect server.
6	Accept GET request to the `/logout` endpoint.

Check Keycloak realm’s OpenID configuration by visiting http://localhost:8080/realms/myrealm/.well-known/openid-configuration.

The previous configuration uses several placeholders. You will need to set up OAUTH_CLIENT_ID, OAUTH_CLIENT_SECRET, OIDC_ISSUER_DOMAIN and KEYCLOAK_REALM environment variables.

export OAUTH_CLIENT_ID=XXXXXXXXXX
export OAUTH_CLIENT_SECRET=YYYYYYYYYY
export OIDC_ISSUER_DOMAIN=ZZZZZ
export KEYCLOAK_REALM=myrealm

You can obtain the realm name, client id and client secret in the Keycloak UI:

We want to use an Authorization Code grant type flow which it is described in the following diagram:

5.6. Home

Create a controller to handle the requests to /. You will display the email of the authenticated person if any. Annotate the controller endpoint with @View since we will use a Thymeleaf template.

src/main/java/example/micronaut/HomeController.java

package example.micronaut;

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import io.micronaut.security.annotation.Secured;
import io.micronaut.security.rules.SecurityRule;
import io.micronaut.views.View;

import java.util.HashMap;
import java.util.Map;

@Controller (1)
public class HomeController {

    @Secured(SecurityRule.IS_ANONYMOUS) (2)
    @View("home") (3)
    @Get (4)
    public Map<String, Object> index() {
        return new HashMap<>();
    }
}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/`.
2	Annotate with `io.micronaut.security.Secured` to configure secured access. The `SecurityRule.IS_ANONYMOUS` expression will allow access without authentication.
3	Use View annotation to specify which template to use to render the response.
4	The @Get annotation maps the `index` method to GET `/` requests.

Create a thymeleaf template:

src/main/resources/views/home.html

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Home</title>
</head>
<body>
<h1>Micronaut - Keycloak example</h1>

<h2 th:if="${security}">username: <span th:text="${security.attributes.get('preferred_username')}"></span></h2>
<h2 th:unless="${security}">username: Anonymous</h2>

<nav>
    <ul>
        <li th:unless="${security}"><a href="/oauth/login/keycloak">Enter</a></li>
        <li th:if="${security}"><a href="/oauth/logout">Logout</a></li>
    </ul>
</nav>
</body>
</html>

Also, note that we return an empty model in the controller. However, we are accessing security in the thymeleaf template.

The SecurityViewModelProcessor injects into the model a security map with the authenticated user. See User in a view documentation.

5.7. EndSessionEndpointResolver

Create an EndSessionEndpointResolver replacement to logout from Keycloak.

src/main/java/example/micronaut/EndSessionEndpointResolverReplacement.java

package example.micronaut;

import io.micronaut.context.BeanContext;
import io.micronaut.context.annotation.Replaces;
import io.micronaut.security.config.SecurityConfiguration;
import io.micronaut.security.oauth2.client.OpenIdProviderMetadata;
import io.micronaut.security.oauth2.configuration.OauthClientConfiguration;
import io.micronaut.security.oauth2.endpoint.endsession.request.EndSessionEndpoint;
import io.micronaut.security.oauth2.endpoint.endsession.request.EndSessionEndpointResolver;
import io.micronaut.security.oauth2.endpoint.endsession.request.OktaEndSessionEndpoint;
import io.micronaut.security.oauth2.endpoint.endsession.response.EndSessionCallbackUrlBuilder;
import io.micronaut.security.token.reader.TokenResolver;
import jakarta.inject.Singleton;

import java.util.Optional;
import java.util.function.Supplier;

@Singleton
@Replaces(EndSessionEndpointResolver.class)
public class EndSessionEndpointResolverReplacement extends EndSessionEndpointResolver {
    private final TokenResolver tokenResolver;
    private final SecurityConfiguration securityConfiguration;
    /**
     * @param beanContext The bean context
     */
    public EndSessionEndpointResolverReplacement(BeanContext beanContext,
                                                 SecurityConfiguration securityConfiguration,
                                                 TokenResolver tokenResolver) {
        super(beanContext);
        this.tokenResolver = tokenResolver;
        this.securityConfiguration = securityConfiguration;
    }

    @Override
    public Optional<EndSessionEndpoint> resolve(OauthClientConfiguration oauthClientConfiguration,
                                                Supplier<OpenIdProviderMetadata> openIdProviderMetadata,
                                                EndSessionCallbackUrlBuilder endSessionCallbackUrlBuilder) {
        return Optional.of(new OktaEndSessionEndpoint(endSessionCallbackUrlBuilder,
                oauthClientConfiguration,
                openIdProviderMetadata,
                securityConfiguration,
                tokenResolver));
    }

}

6. Running the Application

To run the application, use the ./mvnw mn:run command, which starts the application on port 8081.

7. Generate a Micronaut Application Native Executable with GraalVM

We will use GraalVM, the polyglot embeddable virtual machine, to generate a native executable of our Micronaut application.

Compiling native executables ahead of time with GraalVM improves startup time and reduces the memory footprint of JVM-based applications.

Only Java and Kotlin projects support using GraalVM’s native-image tool. Groovy relies heavily on reflection, which is only partially supported by GraalVM.

7.1. Native executable generation

The easiest way to install GraalVM on Linux or Mac is to use SDKMan.io.

Java 11

sdk install java 22.3.r11-grl

If you still use Java 8, use the JDK11 version of GraalVM.

Java 17

sdk install java 22.3.r17-grl

For installation on Windows, or for manual installation on Linux or Mac, see the GraalVM Getting Started documentation.

After installing GraalVM, install the native-image component, which is not installed by default:

gu install native-image

To generate a native executable using Maven, run:

./mvnw package -Dpackaging=native-image

The native executable is created in the target directory and can be run with target/micronautguide.

After you execute the native image, navigate to localhost:8081 and authenticate with Keycloak.

8. Next steps

Read Micronaut OAuth 2.0 documentation to learn more.

Checkout Keycloak website.

9. Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.

Table of Contents

Secure a Micronaut application with Keycloak

1. Getting Started

2. What you will need

3. Solution

4. Run Keycloak on Docker

5. Writing the Application

5.1. Dev default environment

5.2. Start in Port 8081

5.3. Views

5.4. OAuth 2.0

5.5. OAuth 2.0 Configuration

5.6. Home

5.7. EndSessionEndpointResolver

6. Running the Application

7. Generate a Micronaut Application Native Executable with GraalVM

7.1. Native executable generation

8. Next steps

9. Help with the Micronaut Framework