Secure a Micronaut application with Github

Learn how to create a Micronaut application and secure it with an Authorization Server provided by Github. Learn how to write your own Authentication Mapper.

Authors: Sergio del Amo

Micronaut Version: 3.7.0

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:

  • 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 \
    --features=views-thymeleaf,security-oauth2,security-jwt,reactor \
    --build=maven --lang=kotlin
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.

If you use Micronaut Launch, select Micronaut Application as application type and add views-thymeleaf, security-oauth2, security-jwt, and reactor features.

If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features and apply those changes to your application.

4.1. Enable annotation Processing

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



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.

We’ll use the Thymeleaf Java template engine to render views.

4.3. 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.

package example.micronaut

import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
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 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:

<!DOCTYPE html>
<html xmlns:th="">
<h1>Micronaut - Github example</h1>

<h2 th:if="${security}">username: <span th:text="${}"> </h2>
<h2 th:unless="${security}">username: Anonymous</h2>

        <li th:unless="${security}"><a href="/oauth/login/github">Enter</a></li>
        <li th:if="${security}"><a href="/repos">View Repos</a></li>
        <li th:if="${security}"><a href="/logout">Logout</a></li>

Also, note that we return an empty model in the controller. However, we are accessing security in the Thymeleaf template.

4.4. GitHub OAuth App

To provide authentication, create a GitHub OAuth App.

github 1
github 2
github 3

4.5. OAuth 2.0 Configuration

Add the following OAuth2 Configuration:

    authentication: cookie (1)
            generator: (2)
              secret: '"${JWT_GENERATOR_SIGNATURE_SECRET:pleaseChangeThisSecretForANewOne}"' (3)
        github: (4)
          client-id:  '${OAUTH_CLIENT_ID:xxx}' (5)
          client-secret: '${OAUTH_CLIENT_SECRET:yyy}' (6)
          scopes: (7)
            - user:email
            - read:user
            - public_repo
            url: '' (8)
            url: '' (9)
            auth-method: CLIENT_SECRET_POST
        get-allowed: true (10)
1 Once validated, we will save the ID Token in a Cookie. To read in subsequent requests, set to cookie.
2 You can create a SecretSignatureConfiguration named generator via configuration as illustrated above. The generator signature is used to sign the issued JWT claims.
3 Change this to your own secret and keep it safe (do not store this in your VCS).
4 The provider identifier must match the last part of the URL you entered as a redirect URL: /oauth/callback/github.
5 Client Secret. See previous screenshot.
6 Client ID. See previous screenshot.
7 Specify the scopes you want to request. GitHub Scopes let you sepcify exactly what type of access you need.
8 Map manually the GitHub Authorization endpoint.
9 Map manually the Github Token endpoint.
10 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 environment variables.


4.6. User Details Mapper

Here is a high level diagram of how the authorization code grant flow works with an OAuth 2.0 provider such as GitHub.

standard oauth

We need an HTTP Client to retrieve the user info. Create a POJO to represent a GitHub user:

package example.micronaut

import io.micronaut.core.annotation.Introspected

data class GithubUser(val login: String, val name: String, val email: String)

Then, create a Micronaut Declarative HTTP Client to consume GitHub REST API v3

package example.micronaut

import io.micronaut.core.annotation.Nullable
import io.micronaut.http.HttpHeaders
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Header
import io.micronaut.http.annotation.Headers
import io.micronaut.http.annotation.QueryValue
import io.micronaut.http.client.annotation.Client
import org.reactivestreams.Publisher
import javax.validation.constraints.Pattern

    Header(name = "User-Agent", value = ""),
    Header(name = "Accept", value = "application/vnd.github.v3+json, application/json") (1)
@Client(id = "githubv3") (2)
interface GithubApiClient {

    @Get("/user") (3)
    fun getUser(@Header(HttpHeaders.AUTHORIZATION) (5)
                authorization: String?): Publisher<GithubUser> (4)
1 GitHub encourages explicitly requesting version 3 via the Accept header. With @Header, you add the Accept: application/vnd.github.v3+json HTTP header to every request.
2 Add the id githubv3 to the @Client annotation. Later, you will provide URL for this client id.
3 Define a HTTP GET request to /user endpoint.
4 You can return reactive types in a Micronaut declarative HTTP client.
5 You can specify that a parameter binds to a HTTP Header such as the Authorization header.

Specify the URL for the githubv3 service.

        url: ""

For GitHub we need to provide a Authentication Mapper. The easiest way is to create a bean which implements OauthAuthenticationMapper.

package example.micronaut

import io.micronaut.core.annotation.Nullable
import jakarta.inject.Named
import jakarta.inject.Singleton
import org.reactivestreams.Publisher
import reactor.core.publisher.Mono

@Named("github") (1)
class GithubAuthenticationMapper(private val apiClient: GithubApiClient) : OauthAuthenticationMapper {

    override fun createAuthenticationResponse(tokenResponse: TokenResponse,
                                              @Nullable state: State): Publisher<AuthenticationResponse> =
        Mono.from(apiClient.getUser(TOKEN_PREFIX + tokenResponse.accessToken)) (2)
                .map { (login): GithubUser -> AuthenticationResponse.success(login,
                        mapOf(OauthAuthenticationMapper.ACCESS_TOKEN_KEY to tokenResponse.accessToken)) (3)

    companion object {
        const val TOKEN_PREFIX = "token "
        const val ROLE_GITHUB = "ROLE_GITHUB"
1 Usa a name qualifier for the bean which matches the name you used in the OAuth 2.0 configuration in application.yml
2 Consume the /user endpoint with the Micronaut HTTP Client.
3 Save the original GitHub access token in a claim. We will use it to contact GitHub’s API later.

4.7. Retrieve User GitHub repositories

With the access token, we retrieved during the login we will contact the GitHub API to fetch the user’s repositories.

First, create a POJO to represent a GitHub repository:

package example.micronaut

import io.micronaut.core.annotation.Introspected

data class GithubRepo(val name: String)

Add a method to GithubApiClient

    @Get("/user/repos{?sort,direction}") (1)
    fun repos(
            @Pattern(regexp = "created|updated|pushed|full_name") @Nullable @QueryValue sort: String?, (2)
            @Pattern(regexp = "asc|desc") @Nullable @QueryValue direction: String?, (2)
            @Header(HttpHeaders.AUTHORIZATION) authorization: String?): List<GithubRepo>
1 Specify two query values sort and direction.
2 Annotate sort and direction as @Nullable since they are optional. You can restrict the allowed values with use of constraints.

Create a controller to expose /repos endpoint:

package example.micronaut

import io.micronaut.http.HttpHeaderValues
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.views.View

@Controller("/repos") (1)
class ReposController(private val githubApiClient: GithubApiClient) {

    @Secured(SecurityRule.IS_AUTHENTICATED) (2)
    @View("repos") (3)
    @Get (4)
    fun index(authentication: Authentication): Map<String, Any> {
        val repos = githubApiClient.repos(CREATED, DESC, authorizationValue(authentication)) (5)
        return mutableMapOf(REPOS to repos)

    private fun authorizationValue(authentication: Authentication): String? {
        val claim = authentication.attributes[ACCESS_TOKEN_KEY] (6)
        return if (claim is String) {
            HttpHeaderValues.AUTHORIZATION_PREFIX_BEARER + ' ' + claim
        } else null

    companion object {
        const val CREATED = "created"
        const val DESC = "desc"
        const val REPOS = "repos"
1 Qualify the @Controller annotation with /repos to designate the endpoint URL.
2 We want this endpoint to be only accessible to authenticated users.
3 We specify the view name repos which renders the model.
4 Declare a GET endpoint.
5 Consume the GitHub API.
6 Use the previously obtained access token to get access against the GitHub API.

Create a Thymeleaf template:

<!DOCTYPE html>
<html xmlns:th="">
<h1><a href="/">Home</a> &rarr; Repositories</h1>
    <ul th:each="repo: ${repos}">
        <li th:text="${}"/>

5. Running the Application

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


6. 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.

6.1. Native executable generation

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

Java 11
sdk install java 22.1.0.r11-grl
If you still use Java 8, use the JDK11 version of GraalVM.
Java 17
sdk install java 22.1.0.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 executable using Maven, run:

./mvnw package -Dpackaging=native-image

The native executable is created in the target directory and can be run with target/micronautguide.

Visit localhost:8080 and authenticate with GitHub

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.