Secure a Micronaut application with Cognito

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

Authors: Sergio del Amo

Micronaut Version: 3.2.7

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.

4. 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=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.

4.1. Enable annotation Processing

If you use Java or Kotlin and IntelliJ IDEA, make sure to enable annotation processing.

annotationprocessorsintellij

4.2. 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>

4.3. OAuth 2.0

To provide authentication, sign in to your AWS account and go to AWS Cognito.

With the Amazon Cognito SDK, you just write a few lines of code to enable your users to sign-up and sign-in to your mobile and web apps.

Standards-based authentication

Amazon Cognito uses common identity management standards including OpenID Connect, OAuth 2.0, and SAML 2.0.

First, create an Amazon Cognito User Pool:

Amazon Cognito User Pools - A directory for all your users

You can quickly create your own directory to sign up and sign in users, and to store user profiles using Amazon Cognito User Pools. User Pools provide a user interface you can customize to match your application. User Pools also enable easy integration with social identity providers such as Facebook, Google, and Amazon, and enterprise identity providers such as Microsoft Active Directory through SAML.

aws cognito 1
aws cognito 2

Amazon Cognito Pools are regional. Thus, annotate the region you are using.

While you setup the Amazon Cognito User Pool, you will need to save the pool id:

aws cognito 3

Save the client id and client secret:

aws cognito 4

Configure the appropriate callback, make sure you allow Authorization code grant OAuth Flow, and also the scopes openid and email are selected.

aws cognito 5

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>

Add the following OAuth2 Configuration:

src/main/resources/application.yml
micronaut:
  security:
    authentication: idtoken (1)
    oauth2:
      clients:
        cognito: (2)
          client-id: '${OAUTH_CLIENT_ID:xxx}' (3)
          client-secret: '${OAUTH_CLIENT_SECRET:yyy}' (4)
          openid:
            issuer: 'https://cognito-idp.${COGNITO_REGION:us-east-1}.amazonaws.com/${COGNITO_POOL_ID:12345}/' (5)
    endpoints:
      logout:
        get-allowed: true (6)
1 Set micronaut.security.authentication as idtoken. The idtoken provided by Cognito 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 Cognito. JWKS is exposed by the jws-uri entry of Cognito .well-known/openid-configuration
2 The provider identifier should match the last part of the URL you entered as a redirect URL /oauth/callback/cognito
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 pool id and region mentioned previously.
6 Accept GET request to the /logout endpoint.

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

export OAUTH_CLIENT_ID=XXXXXXXXXX
export OAUTH_CLIENT_SECRET=YYYYYYYYYY
export COGNITO_REGION=eu-west-1
export COGNITO_POOL_ID=eu-west-XXCCCAZZZ

Although undocumented in the Amazon Cognito User Pools Auth API Reference, Cognito provides an openid-configuration endpoint which the Micronaut framework uses to configure your application.

https://cognito-idp.{region}.amazonaws.com/{userPoolId}/.well-known/openid-configuration

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

diagramm

4.4. 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 - Cognito 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="${security}"><a href="/oauth/login/cognito">Enter</a></li>
        <li th:if="${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.

5. Running the Application

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

cognitovideo

6. Generate a Micronaut Application Native Image with GraalVM

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

Compiling native images 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.

6.1. Native image generation

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

Java 11
$ sdk install java 21.3.0.r11-grl
If you still use Java 8, use the JDK11 version of GraalVM.
Java 17
$ sdk install java 21.3.0.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 image using Maven, run:

./mvnw package -Dpackaging=native-image

The native image is created in the target directory and can be run with target/application.

After you execute the native image, navigate to localhost:8080 and authenticate with Cognito.

7. Next steps

Read Micronaut OAuth 2.0 documentation to learn more.

8. Help with the Micronaut Framework

Object Computing, Inc. (OCI) sponsored the creation of this Guide. A variety of consulting and support services are available.