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: 3.9.2

1. Getting Started

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

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. 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 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.

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

5. Writing the Application

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

mn create-app example.micronaut.micronautguide --build=maven --lang=groovy

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.

Setup IntelliJ IDEA to develop Micronaut Applications.

5.1. Dependencies

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 Micronaut JWT support dependencies:

pom.xml

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

5.2. Configuration

Add the following OAuth2 Configuration:

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

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 the 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. 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/groovy/example/micronaut/HomeController.groovy

package example.micronaut

import groovy.transform.CompileStatic
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

@CompileStatic
@Controller (1)
class HomeController {

    @Secured(SecurityRule.IS_ANONYMOUS) (2)
    @View('home') (3)
    @Get (4)
    Map<String, Object> index() {
        [:]
    }
}

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 `/`.

5.5. 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.

6. Running the Application

To run the application, use the ./mvnw mn:run command, which starts the application on port 8080.

7. Next steps

Read Micronaut OAuth 2.0 documentation to learn more.

8. 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 Auth0

1. Getting Started

2. What you will need

3. Solution

4. OAuth 2.0

5. Writing the Application

5.1. Dependencies

5.2. Configuration

5.3. Views

5.4. Home controller

5.5. Thymeleaf template

6. Running the Application

7. Next steps

8. Help with the Micronaut Framework