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, Álvaro Sánchez-Mariscal

Micronaut Version: 4.6.3

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 (e.g. IntelliJ IDEA)
JDK 21 or greater installed with JAVA_HOME configured appropriately

3. Amazon Web Services (AWS)

If you don’t have one already, create an AWS Account.

3.1. AWS CLI

Follow the AWS documentation for installing or updating the latest version of the AWS CLI.

3.2. Administrator IAM user

Instead of using your AWS root account, it is recommended that you use an IAM administrative user. If you don’t have one already, follow the steps below to create one:

aws iam create-group --group-name Administrators
aws iam create-user --user-name Administrator
aws iam add-user-to-group --user-name Administrator --group-name Administrators
aws iam attach-group-policy --group-name Administrators --policy-arn $(aws iam list-policies --query 'Policies[?PolicyName==`AdministratorAccess`].{ARN:Arn}' --output text)
aws iam create-access-key --user-name Administrator

Then, run aws configure to configure your AWS CLI to use the Administrator IAM user just created.

4. 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

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=java

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.

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. 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.

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:

Save the client id and client secret:

6.2. Add a domain

6.3. Using the AWS CLI

Some of the following commands use jq

jq is a lightweight and flexible command-line JSON processor

Alternatively, you can use the AWS CLI to create the user pool and client (change the region to your desired value):

export COGNITO_REGION=eu-west-1
export COGNITO_POOL_ID=$(aws cognito-idp create-user-pool --pool-name "Micronaut Guides" --username-attributes "email" --auto-verified-attributes "email" | jq -r '.UserPool.Id')
export OAUTH_CLIENT_ID=$(aws cognito-idp create-user-pool-client --generate-secret --user-pool-id $COGNITO_POOL_ID --client-name "AWS Cognito Micronaut Tutorial" --callback-urls "http://localhost:8080/oauth/callback/cognito" --logout-urls "http://localhost:8080/logout" --supported-identity-providers COGNITO --allowed-o-auth-flows "code" --allowed-o-auth-scopes "phone" "email" "openid" "profile" "aws.cognito.signin.user.admin" --allowed-o-auth-flows-user-pool-client | jq -r '.UserPoolClient.ClientId')
export OAUTH_CLIENT_SECRET=$(aws cognito-idp describe-user-pool-client --user-pool-id $COGNITO_POOL_ID --client-id $OAUTH_CLIENT_ID | jq -r '.UserPoolClient.ClientSecret')
export COGNITO_DOMAIN="micronaut-guides-$RANDOM"
aws cognito-idp create-user-pool-domain --domain $COGNITO_DOMAIN --user-pool-id $COGNITO_POOL_ID

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

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")

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

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 must 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. If you used the AWS CLI, then you are all set.

Otherwise, 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.

curl https://cognito-idp.${COGNITO_REGION}.amazonaws.com/${COGNITO_POOL_ID}/.well-known/openid-configuration

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

6.4. 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.

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

7. Running the Application

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

8. 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.

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

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 21

sdk install 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('-Ob') (2)
        }
    }
}

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 Cognito.

8.3. Cleanup

Once you are done with this guide, you can stop/delete the AWS resources created to avoid incurring unnecessary charges.

aws cognito-idp delete-user-pool-domain --domain $COGNITO_DOMAIN --user-pool-id $COGNITO_POOL_ID
aws cognito-idp delete-user-pool-client --client-id $OAUTH_CLIENT_ID --user-pool-id $COGNITO_POOL_ID
aws cognito-idp delete-user-pool --user-pool-id $COGNITO_POOL_ID

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…).

Table of Contents

Secure a Micronaut application with Cognito

1. Getting Started

2. What you will need

3. Amazon Web Services (AWS)

3.1. AWS CLI

3.2. Administrator IAM user

4. Solution

5. Writing the Application

6. Views

6.1. OAuth 2.0

6.2. Add a domain

6.3. Using the AWS CLI

6.4. Home

7. Running the Application

8. Generate a Micronaut Application Native Executable with GraalVM

8.1. GraalVM Installation

8.2. Native Executable Generation

8.3. Cleanup

9. Next Steps

10. Help with the Micronaut Framework

11. License