Secure a Micronaut app with Github

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

Authors: Sergio del Amo

Micronaut Version: 2.0.0.RC1

1 Getting Started

This guide uses Micronaut 2.x. You can read this tutorial for Micronaut 1.x.

In this guide we are going to create a Micronaut app written in Java.

1.1 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

1.2 Solution

We recommend you to follow the instructions in the next sections and create the app step by step. However, you can go right to the completed example.

Download and unzip the source

Clone the Git repository: git clone https://github.com/micronaut-guides/micronaut-oauth2-github.git

Then, cd into the complete folder which you will find in the root project of the downloaded/cloned project.

2 Writing the App

Create an app using the Micronaut Command Line Interface.

mn create-app example.micronaut.complete

The previous command creates a micronaut app with the default package example.micronaut in a folder named complete.

By default, create-app creates a Java Micronaut app that uses the Gradle build system. However, you could use other build tools such as Maven or other programming languages such as Groovy or Kotlin.

If you are using Java or Kotlin and IntelliJ IDEA make sure you have enabled annotation processing.

2.1 Views

Although Micronaut 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 within a Micronaut Application add the following dependency on your classpath. For example, in build.gradle

build.gradle

dependencies {
  ...
  ..
    implementation("io.micronaut.views:micronaut-views-thymeleaf")
}

2.2 Home

Create a controller to handle the requests to /. You are going to display the email of the authenticated person if any. Annotate the controller endpoint with @View since we are going to 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
public class HomeController {

    @Secured(SecurityRule.IS_ANONYMOUS)
    @View("home")
    @Get
    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 would you like to render the response against.
4	The @Get annotation is used to map 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.

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

2.3 Github OAuth App

To provide authentication, create a Github Oauth App.

2.4 OAuth 2.0 Configuration

To use OAuth 2.0 integration, add the next dependency:

build.gradle

dependencies {
  ...
  ..
    implementation("io.micronaut.security:micronaut-security-oauth2")
}

Add the following Oauth2 Configuration: Add also JWT Micronaut’s JWT support dependencies:

build.gradle

dependencies {
  ...
  ..
    annotationProcessor("io.micronaut.security:micronaut-security-annotations")
    implementation("io.micronaut.security:micronaut-security-jwt")
}

Add the following Oauth2 Configuration:

src/main/resources/application.yml

micronaut:
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}' (5)
          client-secret: '${OAUTH_CLIENT_SECRET}' (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 are going to 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 by 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’s Authorization endpoint.
9	Map manually the Github’s Token endpoint.
10	Accept GET request to the `/logout` endpoint.

The previous configuration uses several placeholders. You will need to setup OAUTH_CLIENT_ID, OAUTH_CLIENT_SECRET environment variables.

export OAUTH_CLIENT_ID=XXXXXXXXXX
export OAUTH_CLIENT_SECRET=YYYYYYYYYY

2.5 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.

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

src/main/java/example/micronaut/GithubUser.java

package example.micronaut;

import com.fasterxml.jackson.databind.PropertyNamingStrategy;
import com.fasterxml.jackson.databind.annotation.JsonNaming;
import io.micronaut.core.annotation.Introspected;

@Introspected
public class GithubUser {

    private String login;
    private String name;
    private String email;

    public GithubUser() {

    }

    public String getLogin() {
        return login;
    }

    public void setLogin(String login) {
        this.login = login;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

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

src/main/java/example/micronaut/GithubApiClient.java

package example.micronaut;

import io.micronaut.http.HttpHeaders;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Header;
import io.micronaut.http.annotation.QueryValue;
import io.micronaut.http.client.annotation.Client;
import io.reactivex.Flowable;

import javax.annotation.Nullable;
import javax.validation.constraints.Pattern;
import java.util.List;

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

    @Get("/user") (3)
    Flowable<GithubUser> getUser( (4)
            @Header(HttpHeaders.AUTHORIZATION) String authorization); (5)
}

1	Github encourages to explicitly request the 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 UserDetails Mapper. The easiest way is to create a bean which implements OauthUserDetailsMapper.

src/main/java/example/micronaut/GithubUserDetailsMapper.java

package example.micronaut;
import io.micronaut.security.authentication.UserDetails;
import io.micronaut.security.oauth2.endpoint.token.response.OauthUserDetailsMapper;
import io.micronaut.security.oauth2.endpoint.token.response.TokenResponse;
import org.reactivestreams.Publisher;

import javax.inject.Named;
import javax.inject.Singleton;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@Named("github") (1)
@Singleton
public class GithubUserDetailsMapper implements OauthUserDetailsMapper {

    public static final String TOKEN_PREFIX = "token ";
    public static final String ROLE_GITHUB = "ROLE_GITHUB";
    private final GithubApiClient apiClient;

    public GithubUserDetailsMapper(GithubApiClient apiClient) {
        this.apiClient = apiClient;
    }

    @Override
    public Publisher<UserDetails> createUserDetails(TokenResponse tokenResponse) {
        return apiClient.getUser(TOKEN_PREFIX + tokenResponse.getAccessToken()) (2)
                .map(user -> new UserDetails(user.getLogin(),
                        Collections.singletonList(ROLE_GITHUB),
                        Collections.singletonMap(OauthUserDetailsMapper.ACCESS_TOKEN_KEY, tokenResponse.getAccessToken()))); (3)
    }
}

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 to to contact Github’s api later.

2.6 Retrieve User Github repositories

With the access token, we retrieved during the login we are going to contact the Github API to fetch the user’s repositories.

First, create a POJO to represent a Github repository:

src/main/java/example/micronaut/GithubRepo.java

package example.micronaut;

import io.micronaut.core.annotation.Introspected;

@Introspected
public class GithubRepo {

    private String name;

    public GithubRepo() {

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Add a method to GithubApiClient

....
public interface GithubApiClient {
....
    @Get("/user/repos{?sort,direction}") (1)
    List<GithubRepo> repos(
            @Pattern(regexp = "created|updated|pushed|full_name") @Nullable @QueryValue String sort, (2)
            @Pattern(regexp = "asc|desc") @Nullable @QueryValue String direction, (2)
            @Header(HttpHeaders.AUTHORIZATION) String authorization);
}

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/java/example/micronaut/ReposController.java

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.OauthUserDetailsMapper;
import io.micronaut.security.rules.SecurityRule;
import io.micronaut.views.View;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@Controller("/repos") (1)
public class ReposController {

    public static final String CREATED = "created";
    public static final String DESC = "desc";
    public static final String REPOS = "repos";
    private final GithubApiClient githubApiClient;

    public ReposController(GithubApiClient githubApiClient) {
        this.githubApiClient = githubApiClient;
    }

    @Secured(SecurityRule.IS_AUTHENTICATED) (2)
    @View("repos") (3)
    @Get (4)
    Map<String, Object> index(Authentication authentication) {
        List<GithubRepo> repos = githubApiClient.repos(CREATED, DESC, authorizationValue(authentication));  (5)
        Map<String, Object> model = new HashMap<>();
        model.put(REPOS, repos);
        return model;
    }

    private String authorizationValue(Authentication authentication) {
        String authorization = null;
        Object claim = authentication.getAttributes().get(OauthUserDetailsMapper.ACCESS_TOKEN_KEY);  (6)
        if (claim instanceof String) {
            authorization = HttpHeaderValues.AUTHORIZATION_PREFIX_BEARER + " " + claim.toString();
        }
        return authorization;
    }
}

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 is used to render 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>

3 Running the Application

To run the application use the ./gradlew run command which will start the application on port 8080.

4 Learn More

Read Micronaut OAuth 2.0 documentation to learn more.

5 Help with Micronaut

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

OCI is Home to Micronaut.

Meet the Team