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: 3.2.7

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 --features=security-oauth2,security-jwt,views-thymeleaf,reactor,graalvm example.micronaut.micronautguide --build=gradle --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.

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

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

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.

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.

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.

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 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 - Github example</h1>

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

<nav>
    <ul>
        <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>
    </ul>
</nav>
</body>
</html>

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:

src/main/resources/application.yml
micronaut:
  security:
    authentication: cookie (1)
    token:
      jwt:
        signatures:
          secret:
            generator: (2)
              secret: '"${JWT_GENERATOR_SIGNATURE_SECRET:pleaseChangeThisSecretForANewOne}"' (3)
    oauth2:
      clients:
        github: (4)
          client-id:  '${OAUTH_CLIENT_ID:xxx}' (5)
          client-secret: '${OAUTH_CLIENT_SECRET:yyy}' (6)
          scopes: (7)
            - user:email
            - read:user
            - public_repo
          authorization:
            url: 'https://github.com/login/oauth/authorize' (8)
          token:
            url: 'https://github.com/login/oauth/access_token' (9)
            auth-method: CLIENT_SECRET_POST
    endpoints:
      logout:
        get-allowed: true (10)
1 Once validated, we will save the ID Token in a Cookie. To read in subsequent requests, set micronaut.security.authentication 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 should 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.

export OAUTH_CLIENT_ID=XXXXXXXXXX
export OAUTH_CLIENT_SECRET=YYYYYYYYYY

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:

src/main/kotlin/example/micronaut/GithubUser.kt
package example.micronaut

import io.micronaut.core.annotation.Introspected

@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

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

@Headers(
    Header(name = "User-Agent", value = "https://micronautguides.com"),
    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.

src/main/resources/application.yml
micronaut:
  http:
    services:
      githubv3:
        url: "https://api.github.com"

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

src/main/kotlin/example/micronaut/GithubAuthenticationMapper.kt
package example.micronaut

import io.micronaut.core.annotation.Nullable
import io.micronaut.security.authentication.AuthenticationResponse
import io.micronaut.security.oauth2.endpoint.authorization.state.State
import io.micronaut.security.oauth2.endpoint.token.response.OauthAuthenticationMapper
import io.micronaut.security.oauth2.endpoint.token.response.TokenResponse
import jakarta.inject.Named
import jakarta.inject.Singleton
import org.reactivestreams.Publisher
import reactor.core.publisher.Mono

@Named("github") (1)
@Singleton
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,
                        listOf(ROLE_GITHUB),
                        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:

src/main/kotlin/example/micronaut/GithubRepo.kt
package example.micronaut

import io.micronaut.core.annotation.Introspected

@Introspected
data class GithubRepo(val name: String)

Add a method to GithubApiClient

src/main/kotlin/example/micronaut/GithubApiClient.kt
    @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:

src/main/kotlin/example/micronaut/ReposController.kt
package example.micronaut

import io.micronaut.http.HttpHeaderValues
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.security.annotation.Secured
import io.micronaut.security.authentication.Authentication
import io.micronaut.security.oauth2.endpoint.token.response.OauthAuthenticationMapper.ACCESS_TOKEN_KEY
import io.micronaut.security.rules.SecurityRule
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:

src/main/resources/views/repos.html
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Home</title>
</head>
<body>
<h1><a href="/">Home</a> &rarr; Repositories</h1>
<nav>
    <ul th:each="repo: ${repos}">
        <li th:text="${repo.name}"/>
    </ul>
</nav>
</body>
</html>

5. Running the Application

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

video

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 Gradle, run:

./gradlew nativeCompile

The native image is created in build/native/nativeCompile directory and can be run with build/native/nativeCompile/application.

It is possible to customize the name of the native image or pass additional parameters to GraalVM:

build.gradle
graalvmNative {
    binaries {
        main {
            imageName.set('mn-graalvm-application') (1)
            buildArgs.add('--verbose') (2)
        }
    }
}
1 The native image name will now be mn-graalvm-application
2 It is possible to pass extra arguments to build the native image

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

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