These tutorials target Micronaut Framework 3. Read, Guides for Micronaut Framework 4.

Table of Contents

Micronaut Security API Key

Learn how to secure a Micronaut application using an API Key.

Authors: Sergio del Amo

Micronaut Version: 3.9.2

1. Getting Started

In this guide, you will create a Micronaut application written in Java and secure it with an API Key.

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=security,graalvm \
    --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.

If you use Micronaut Launch, select Micronaut Application as application type and add security, and graalvm 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.

Setup IntelliJ IDEA to develop Micronaut Applications.

4.1. ApiKey Repository

To keep things simple, populate API keys via configuration.

src/main/java/example/micronaut/ApiKeyConfiguration.java
package example.micronaut;

import io.micronaut.context.annotation.EachProperty;
import jakarta.annotation.Nonnull;

@EachProperty("api-keys") (1)
public interface ApiKeyConfiguration {

    @Nonnull
    String getName();

    @Nonnull
    String getKey();
}
1 The @EachProperty annotation creates a ConfigurationProperties bean for each sub-property within the given name.

Create a functional interface to retrieve a user given an API Key.

src/main/java/example/micronaut/ApiKeyRepository.java
package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import javax.validation.constraints.NotBlank;
import java.security.Principal;
import java.util.Optional;

@FunctionalInterface (1)
public interface ApiKeyRepository {
    @NonNull
    Optional<Principal> findByApiKey(@NonNull @NotBlank String apiKey);
}
1 An interface with one abstract method declaration is known as a functional interface. The compiler verifies that all interfaces annotated with @FunctionInterface really contain one and only one abstract method.

Create an implementation of ApiKeyRepository which uses the API Keys stored in configuration.

src/main/java/example/micronaut/ApiKeyRepositoryImpl.java
package example.micronaut;

import jakarta.inject.Singleton;
import io.micronaut.core.annotation.NonNull;
import javax.validation.constraints.NotBlank;
import java.security.Principal;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
import java.util.List;

@Singleton (1)
class ApiKeyRepositoryImpl implements ApiKeyRepository {

    private final Map<String, Principal> keys;

    ApiKeyRepositoryImpl(List<ApiKeyConfiguration> apiKeys) {
        keys = new HashMap<>();
        for (ApiKeyConfiguration configuration : apiKeys) {
            keys.put(configuration.getKey(), configuration::getName);
        }
        System.out.println("Keys #" + keys.keySet().size());
    }

    @Override
    @NonNull
    public Optional<Principal> findByApiKey(@NonNull @NotBlank String apiKey) {
        return Optional.ofNullable(keys.get(apiKey));
    }
}
1 Use jakarta.inject.Singleton to designate a class as a singleton.

4.2. Token Reader

Micronaut Security is flexible. You define a bean of type TokenReader to read tokens from a custom HTTP Header such as X-API-Key.

src/main/java/example/micronaut/ApiKeyTokenReader.java
package example.micronaut;

import io.micronaut.security.token.reader.HttpHeaderTokenReader;
import jakarta.inject.Singleton;

@Singleton (1)
public class ApiKeyTokenReader extends HttpHeaderTokenReader { (2)
    private static final String X_API_TOKEN = "X-API-KEY";

    @Override
    protected String getPrefix() {
        return null;
    }

    @Override
    protected String getHeaderName() {
        return X_API_TOKEN;
    }
}
1 Use jakarta.inject.Singleton to designate a class as a singleton.
2 HttpHeaderTokenReader is a convenient abstract class to ease reading a token from an HTTP Header.

4.3. Token Validator

Define a bean of type TokenValidator to validate the API Keys leveraging the ApiKeyRepository.

src/main/java/example/micronaut/ApiKeyTokenValidator.java
package example.micronaut;

import io.micronaut.core.async.publisher.Publishers;
import io.micronaut.http.HttpRequest;
import io.micronaut.security.authentication.Authentication;
import io.micronaut.security.token.validator.TokenValidator;
import jakarta.inject.Singleton;
import org.reactivestreams.Publisher;

@Singleton (1)
class ApiKeyTokenValidator implements TokenValidator  {

    private final ApiKeyRepository apiKeyRepository;

    ApiKeyTokenValidator(ApiKeyRepository apiKeyRepository) { (2)
        this.apiKeyRepository = apiKeyRepository;
    }

    @Override
    public Publisher<Authentication> validateToken(String token, HttpRequest<?> request) {
        if (request == null || !request.getPath().startsWith("/api")) { (3)
            return Publishers.empty();
        }
        return apiKeyRepository.findByApiKey(token)
                .map(principal -> Authentication.build(principal.getName()))
                .map(Publishers::just).orElseGet(Publishers::empty);
    }
}
1 Use jakarta.inject.Singleton to designate a class as a singleton.
2 Use constructor injection to inject a bean of type ApiKeyRepository.
3 You can restrict the validity of an API Key to specific paths.

4.4. Controllers

To test the application create several controllers.

src/main/java/example/micronaut/ApiController.java
package example.micronaut;

import io.micronaut.http.MediaType;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Produces;
import io.micronaut.security.annotation.Secured;
import io.micronaut.security.rules.SecurityRule;

import java.security.Principal;

@Controller("/api") (1)
class ApiController {

    @Produces(MediaType.TEXT_PLAIN) (2)
    @Get (3)
    @Secured(SecurityRule.IS_AUTHENTICATED) (4)
    String index(Principal principal) { (5)
        return "Hello " + principal.getName();
    }
}
1 The class is defined as a controller with the @Controller annotation mapped to the path /api.
2 Set the response content-type to text/plain with the @Produces annotation.
3 The @Get annotation maps the index method to an HTTP GET request on /.
4 Annotate with io.micronaut.security.Secured to configure secured access. The SecurityRule.IS_AUTHENTICATED expression allows only access to authenticated users.
5 You can bind java.security.Principal as a method’s parameter in a controller.

Create tests that verify /api returns 401 if no API Key is present or the request contains a wrong API Key.

src/test/java/example/micronaut/ApiControllerTest.java
package example.micronaut;

import io.micronaut.context.annotation.Property;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.MediaType;
import io.micronaut.http.client.BlockingHttpClient;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.http.client.exceptions.HttpClientResponseException;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.function.Executable;

import java.util.Optional;

import static org.junit.jupiter.api.Assertions.*;

@Property(name = "api-keys.companyA.key", value = "XXX") (1)
@Property(name = "api-keys.companyA.name", value = "John") (1)
@Property(name = "api-keys.companyB.key", value = "YYY") (1)
@Property(name = "api-keys.companyB.name", value = "Paul") (1)
@MicronautTest (2)
class ApiControllerTest {
    @Inject
    @Client("/")
    HttpClient httpClient; (3)

    @Test
    void apiIsSecured() {
        BlockingHttpClient client = httpClient.toBlocking();
        HttpRequest<?> request = HttpRequest.GET("/api").accept(MediaType.TEXT_PLAIN);
        Executable e = () -> client.exchange(request);
        HttpClientResponseException thrown = assertThrows(HttpClientResponseException.class, e);
        assertEquals(HttpStatus.UNAUTHORIZED, thrown.getStatus());
    }

    @Test
    void apiNotAccessibleIfWrongKey() {
        BlockingHttpClient client = httpClient.toBlocking();
        HttpRequest<?> request = createRequest("ZZZ");
        Executable e = () -> client.exchange(request);
        HttpClientResponseException thrown = assertThrows(HttpClientResponseException.class, e);
        assertEquals(HttpStatus.UNAUTHORIZED, thrown.getStatus());
    }

    @Test
    void apiIsAccessibleWithAnApiKey() {
        BlockingHttpClient client = httpClient.toBlocking();

        HttpResponse<String> response = assertDoesNotThrow(() -> client.exchange(createRequest("XXX"), String.class));
        assertEquals(HttpStatus.OK, response.getStatus());
        Optional<String> body = response.getBody();
        assertTrue(body.isPresent());
        assertEquals("Hello John", body.get());

        response = assertDoesNotThrow(() -> client.exchange(createRequest("YYY"), String.class));
        assertEquals(HttpStatus.OK, response.getStatus());
        body = response.getBody();
        assertTrue(body.isPresent());
        assertEquals("Hello Paul", body.get());
    }

    private static HttpRequest<?> createRequest(String apiKey) {
        return HttpRequest.GET("/api")
                .accept(MediaType.TEXT_PLAIN)
                .header("X-API-KEY", apiKey);
    }
}
1 Annotate the class with @Property to supply configuration to the test.
2 Annotate the class with @MicronautTest so the Micronaut framework will initialize the application context and the embedded server. More info.
3 Inject the HttpClient bean and point it to the embedded server.

Create a controller whose path does not match the ApiKeyTokenValidator.

src/main/java/example/micronaut/AppController.java
package example.micronaut;

import io.micronaut.http.MediaType;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.Produces;
import io.micronaut.security.annotation.Secured;
import io.micronaut.security.rules.SecurityRule;

@Controller("/app") (1)
class AppController {

    @Produces(MediaType.TEXT_PLAIN) (2)
    @Secured(SecurityRule.IS_AUTHENTICATED) (3)
    @Get (4)
    String index() {
        return "Top Secret";
    }
}
1 The class is defined as a controller with the @Controller annotation mapped to the path /app.
2 Set the response content-type to text/plain with the @Produces annotation.
3 Annotate with io.micronaut.security.Secured to configure secured access. The SecurityRule.IS_AUTHENTICATED expression allows only access to authenticated users.
4 The @Get annotation maps the index method to an HTTP GET request on /.

Create tests that verify /app returns 401 if no API Key is present or even when the request contains a valid API Key.

src/test/java/example/micronaut/AppControllerTest.java
package example.micronaut;

import io.micronaut.context.annotation.Property;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.MediaType;
import io.micronaut.http.client.BlockingHttpClient;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.http.client.exceptions.HttpClientResponseException;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.function.Executable;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;

@Property(name = "api-keys.companyA.key", value = "XXX") (1)
@Property(name = "api-keys.companyA.name", value = "John") (1)
@MicronautTest (2)
class AppControllerTest {

    @Inject
    @Client("/")
    HttpClient httpClient; (3)

    @Test
    void appIsSecured() {
        BlockingHttpClient client = httpClient.toBlocking();
        HttpRequest<?> request = HttpRequest.GET("/app").accept(MediaType.TEXT_PLAIN);
        Executable e = () -> client.exchange(request);
        HttpClientResponseException thrown = assertThrows(HttpClientResponseException.class, e);
        assertEquals(HttpStatus.UNAUTHORIZED, thrown.getStatus());
    }

    @Test
    void apiKeyNotValidForTopSecret() {
        BlockingHttpClient client = httpClient.toBlocking();
        HttpRequest<?> request = HttpRequest.GET("/app").accept(MediaType.TEXT_PLAIN).header("X-API-KEY", "XXX");

        Executable e = () -> client.exchange(request);
        HttpClientResponseException thrown = assertThrows(HttpClientResponseException.class, e);
        assertEquals(HttpStatus.UNAUTHORIZED, thrown.getStatus());
    }
}
1 Annotate the class with @Property to supply configuration to the test.
2 Annotate the class with @MicronautTest so the Micronaut framework will initialize the application context and the embedded server. More info.
3 Inject the HttpClient bean and point it to the embedded server.

5. Testing the Application

To run the tests:

./mvnw test

5.1. Resources

Set configuration to have an API available when you run your application:

src/main/resources/application.yml
api-keys:
  sdelamo:
    name: Sergio
    key: FOOBAR

6. Running the Application

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

To test the running application, issue a GET request to localhost:8080 providing a valid API Key:

curl -i --header "Accept: text/plain" --header "X-API-KEY: FOOBAR" localhost:8080

7. 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.

7.1. Native executable generation

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

Java 11
sdk install java 22.3.r11-grl
If you still use Java 8, use the JDK11 version of GraalVM.
Java 17
sdk install java 22.3.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.

To test the native executable, issue a GET request to localhost:8080 providing a valid API Key:

curl -i --header "Accept: text/plain" --header "X-API-KEY: FOOBAR" localhost:8080

8. Next steps

See the Micronaut security documentation to learn more.

9. Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.