Table of Contents

Secure a Micronaut application with Auth0

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

Authors: Sergio del Amo

Micronaut Version: 4.6.3

1. Getting Started

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

2. What you will need

To complete this guide, you will need the following:

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.

4. OAuth 2.0

To provide authentication, sign in to your Auth0 account.

Create an Application

auth0 create application

Fill the Application URIs:

auth0 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 allowed web origins.

Once you have an HTTPS domain (e.g. https://myapp.org), enter it as Application Login URI: https://myapp.org/oauth/login/auth0.

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

auth0 clientid clientsecret

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

diagramm

5. 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=kotlin
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.

5.1. 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")

5.2. Configuration

Add the following OAuth2 Configuration:

Since Micronaut Framework 4.0, to use YAML configuration, you have to add the YAML dependency.
src/main/resources/application.yml
  security:
    authentication: idtoken (1)
    oauth2:
      clients:
        auth0: (2)
          client-id: '${OAUTH_CLIENT_ID:xxx}' (3)
          client-secret: '${OAUTH_CLIENT_SECRET:yyy}' (4)
          openid:
            issuer: 'https://${OAUTH_DOMAIN:micronautguides.eu.auth0.com}/' (5)
    endpoints:
      logout:
        get-allowed: true (6)
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 openidconfiguration:

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

6. 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")

6.1. 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.

src/main/kotlin/example/micronaut/HomeController.kt
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

@Controller (1)
class HomeController {

    @Secured(SecurityRule.IS_ANONYMOUS) (2)
    @View("home") (3)
    @Get (4)
    fun index(): Map<String, Any> = 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 /.

6.2. 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.

7. Running the Application

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

auth0video

8. 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.

8.1. GraalVM installation

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

Java 21
sdk install java 21.0.5-graal
Java 21
sdk use java 21.0.5-graal

For installation on Windows, or for 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 21
sdk install java 21.0.2-graalce
Java 21
sdk use java 21.0.2-graalce

8.2. 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') (1)
            buildArgs.add('--verbose') (2)
        }
    }
}
1 The native executable name will now be mn-graalvm-application
2 It is possible to pass extra arguments to build the native executable

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

9. Next steps

Read Micronaut OAuth 2.0 documentation to learn more.

10. Help with the Micronaut Framework

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

11. License

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