Java / Gradle

Secure a Micronaut application with Auth0

Learn how to create a Micronaut application and secure it with an Authorization Server provided by Auth0.

Sergio del Amo

On this guide

In this section

Getting Started

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

What you will need

To complete this guide, you will need the following:

Some time on your hands
A decent text editor or IDE (e.g. IntelliJ IDEA)
JDK 21 or greater installed with JAVA_HOME configured appropriately

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

OAuth 2.0

To provide authentication, sign in to your Auth0 account.

Create an application.

Fill the application URIs:

Enter http://localhost:8080/oauth/callback/auth0 as callback URL.
Enter http://localhost:8080/logout as allowed logout URL.
Enter http://localhost:8080 as the allowed web origin.

Once you have an HTTPS domain (for example, https://myapp.org), enter it as the application login URI: https://myapp.org/oauth/login/auth0.

You can obtain the application’s domain, client id, and secret in the Auth0 console.

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

Writing the Application

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

mn create-app example.micronaut.micronautguide --build=gradle --lang=java

Note	If you don’t specify the `--build` argument, Gradle with the Kotlin DSL is used as the build tool. If you don’t specify the `--lang` argument, Java is used as the language. If you don’t specify the `--test` argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.

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

Setup IntelliJ IDEA to develop Micronaut Applications.

Dependencies

To use OAuth 2.0 integration, add the following dependency:

build.gradle

implementation("io.micronaut.security:micronaut-security-oauth2")

Also add Micronaut JWT support dependencies:

build.gradle

implementation("io.micronaut.security:micronaut-security-jwt")

Configuration

Add the following OAuth 2.0 configuration:

src/main/resources/application.properties

micronaut.security.authentication=idtoken 
# 
micronaut.security.oauth2.clients.auth0.client-id=${OAUTH_CLIENT_ID:xxx} 
micronaut.security.oauth2.clients.auth0.client-secret=${OAUTH_CLIENT_SECRET:yyy} 
micronaut.security.oauth2.clients.auth0.openid.issuer=https://${OAUTH_DOMAIN:micronautguides.eu.auth0.com}/ 
micronaut.security.endpoints.logout.get-allowed=true

1	Set `micronaut.security.authentication` as `idtoken`. The `idtoken` provided by Auth0 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 Auth0. JWKS is exposed by the `jws-uri` entry of Auth0 `.well-known/openid-configuration`.
2	The provider identifier must match the last part of the URL you entered as a redirect URL: `/oauth/callback/auth0`.
3	Client ID. See previous screenshot.
4	Client Secret. See previous screenshot.
5	`issuer` URL. It allows the Micronaut framework to discover the configuration of the OpenID Connect server. Note: we will use the application’s domain.
6	Accept GET request to the `/logout` endpoint.

When you start the Micronaut application, it fetches the Auth0 application’s openid-configuration:

https://{auth0domain}/.well-known/openid-configuration

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

export OAUTH_CLIENT_ID=XXXXXXXXXX
export OAUTH_CLIENT_SECRET=YYYYYYYYYY
export OAUTH_DOMAIN=micronautguides.eu.auth0.com

Views

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

build.gradle

implementation("io.micronaut.views:micronaut-views-thymeleaf")

Home controller

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.

java/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 // 
public class HomeController {

    @Secured(SecurityRule.IS_ANONYMOUS) // 
    @View("home") // 
    @Get // 
    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 an HTTP GET request on `/`.

Thymeleaf template

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 - Auth0 example</h1>

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

<nav>
    <ul>
        <li th:unless="${security}"><a href="/oauth/login/auth0">Enter</a></li>
        <li th:if="${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.

Running the Application

To run the application, use the ./gradlew run command, which starts the application on port 8080.

Generate a Micronaut Application Native Executable with GraalVM

We will use GraalVM, an advanced JDK with ahead-of-time Native Image compilation, to generate a native executable of this Micronaut application.

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

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

GraalVM Installation

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

Java 25

sdk install java 25.0.2-graal

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

The previous command installs Oracle GraalVM, which is free to use in production and free to redistribute, at no cost, under the GraalVM Free Terms and Conditions.

Alternatively, you can use the GraalVM Community Edition:

Java 25

sdk install java 25.0.2-graalce

Native Executable Generation

To generate a native executable using Gradle, run:

./gradlew nativeCompile

The native executable is created in build/native/nativeCompile directory and can be run with build/native/nativeCompile/micronautguide.

It is possible to customize the name of the native executable or pass additional parameters to GraalVM:

build.gradle

graalvmNative {
    binaries {
        main {
            imageName.set('mn-graalvm-application') // 
            buildArgs.add('-Ob') // 
        }
    }
}

1	The native executable name will now be `mn-graalvm-application`
2	It is possible to pass extra build arguments to `native-image`. For example, `-Ob` enables the quick build mode.

After you execute the native executable, navigate to localhost:8080 and authenticate with Auth0.

Next Steps

Read Micronaut OAuth 2.0 documentation to learn more.

Help with the Micronaut Framework

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

License

Note	All guides are released with an Apache License 2.0 for the code and a Creative Commons Attribution 4.0 license for the writing and media (images).