Kotlin / Gradle

Micronaut Basic Auth

Learn how to secure a Micronaut application using 'Basic' HTTP Authentication Scheme.

Sergio del Amo

On this guide

In this section

Getting Started

In this guide, we will create a Micronaut application written in Kotlin and secure it with HTTP Basic Auth.

RFC7617 defines the "Basic" Hypertext Transfer Protocol (HTTP) authentication scheme, which transmits credentials as user-id/password pairs, encoded using Base64.

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

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

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=gradle \
    --lang=kotlin \
    --test=junit

Note	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.

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

Note	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.

Diff

Setup IntelliJ IDEA to develop Micronaut Applications.

Authentication Provider

To keep this guide simple, create a naive AuthenticationProvider to simulate user authentication.

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

package example.micronaut

import io.micronaut.http.HttpRequest
import io.micronaut.security.authentication.AuthenticationFailureReason
import io.micronaut.security.authentication.AuthenticationRequest
import io.micronaut.security.authentication.AuthenticationResponse
import io.micronaut.security.authentication.provider.HttpRequestAuthenticationProvider
import jakarta.inject.Singleton

@Singleton // 
class AuthenticationProviderUserPassword<B : Any> : HttpRequestAuthenticationProvider<B> { // 
    override fun authenticate(
        requestContext: HttpRequest<B>?,
        authenticationRequest: AuthenticationRequest<String?, String?>
    ): AuthenticationResponse {
        return if (authenticationRequest.identity == "sherlock" && authenticationRequest.secret == "password")
            AuthenticationResponse.success(authenticationRequest.identity!!) else
            AuthenticationResponse.failure(AuthenticationFailureReason.CREDENTIALS_DO_NOT_MATCH)
    }
}

1	Use `jakarta.inject.Singleton` to designate a class as a singleton.
2	A Micronaut Authentication Provider implements the interface `io.micronaut.security.authentication.provider.HttpRequestAuthenticationProvider`.

Controllers

Create HomeController which resolves the base URL /:

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

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

@Secured(SecurityRule.IS_AUTHENTICATED) // 
@Controller// 
class HomeController {

    @Produces(MediaType.TEXT_PLAIN)
    @Get // 
    fun index(principal: Principal): String = principal.name // 
}

1	Annotate with `io.micronaut.security.Secured` to configure secured access. The `isAuthenticated()` expression will allow access only to authenticated users.
2	Annotate with `io.micronaut.http.annotation.Controller` to designate the class as a Micronaut controller.
3	You can specify the HTTP verb that a controller action responds to. To respond to a GET request, use the `io.micronaut.http.annotation.Get` annotation.
4	If a user is authenticated, the Micronaut framework will bind the user object to an argument of type `java.security.Principal` (if present).

WWW-Authenticate

Replace the default Exception Handler for AuthorizationExceptionHandler, the exception raised when a request is not authorized.

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

package example.micronaut

import io.micronaut.context.annotation.Replaces
import io.micronaut.http.HttpHeaders.WWW_AUTHENTICATE
import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpResponse
import io.micronaut.http.HttpStatus.FORBIDDEN
import io.micronaut.http.HttpStatus.UNAUTHORIZED
import io.micronaut.http.MutableHttpResponse
import io.micronaut.http.server.exceptions.response.ErrorResponseProcessor
import io.micronaut.security.authentication.AuthorizationException
import io.micronaut.security.authentication.DefaultAuthorizationExceptionHandler
import io.micronaut.security.config.RedirectConfiguration
import io.micronaut.security.config.RedirectService
import io.micronaut.security.errors.PriorToLoginPersistence
import jakarta.inject.Singleton

@Singleton // 
@Replaces(DefaultAuthorizationExceptionHandler::class) // 
class DefaultAuthorizationExceptionHandlerReplacement(
    errorResponseProcessor: ErrorResponseProcessor<*>,
    redirectConfiguration: RedirectConfiguration,
    redirectService: RedirectService,
    priorToLoginPersistence: PriorToLoginPersistence<*, *>?
) : DefaultAuthorizationExceptionHandler(
    errorResponseProcessor, redirectConfiguration, redirectService, priorToLoginPersistence
) {

    override fun httpResponseWithStatus(
        request: HttpRequest<*>,
        e: AuthorizationException
    ): MutableHttpResponse<*> =
        if (e.isForbidden) {
            HttpResponse.status<Any>(FORBIDDEN);
        } else {
            HttpResponse.status<Any>(UNAUTHORIZED)
                .header(WWW_AUTHENTICATE, "Basic realm=\"Micronaut Guide\"")
        }
}

The previous code adds the WWW-Authenticate header to indicate the authentication scheme.

1	Use `jakarta.inject.Singleton` to designate a class as a singleton.
2	Specify that `DefaultAuthorizationExceptionHandlerReplacement` replaces the bean `DefaultAuthorizationExceptionHandler`

Tests

Create a test to verify the user authentication flow via Basic Auth.

kotlin/src/test/kotlin/example/micronaut/BasicAuthTest.kt

package example.micronaut

import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpStatus.OK
import io.micronaut.http.HttpStatus.UNAUTHORIZED
import io.micronaut.http.MediaType.TEXT_PLAIN
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.Assertions.assertEquals
import org.junit.jupiter.api.Assertions.assertThrows
import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.function.Executable

@MicronautTest // 
class BasicAuthTest(@Client("/") val client: HttpClient) { // 

    @Test
    fun verifyHttpBasicAuthWorks() {
        //when: 'Accessing a secured URL without authenticating'
        val e = Executable { client.toBlocking().exchange<Any, Any>(HttpRequest.GET<Any>("/").accept(TEXT_PLAIN)) } // 

        // then: 'returns unauthorized'
        val thrown = assertThrows(HttpClientResponseException::class.java, e) // 
        assertEquals(UNAUTHORIZED, thrown.status)

        assertTrue(thrown.response.headers.contains("WWW-Authenticate"))
        assertEquals("Basic realm=\"Micronaut Guide\"", thrown.response.headers.get("WWW-Authenticate"))

        //when: 'A secured URL is accessed with Basic Auth'
        val rsp = client.toBlocking().exchange(HttpRequest.GET<Any>("/")
                .accept(TEXT_PLAIN)
                .basicAuth("sherlock", "password"), // 
                String::class.java) // 
        //then: 'the endpoint can be accessed'
        assertEquals(OK, rsp.status)
        assertEquals("sherlock", rsp.body.get()) // 
    }
}

1	Annotate the class with `@MicronautTest` so the Micronaut framework will initialize the application context and the embedded server. More info.
2	Inject the `HttpClient` bean and point it to the embedded server.
3	Creating HTTP Requests is easy thanks to the Micronaut framework fluid API.
4	If you attempt to access a secured endpoint without authentication, 401 is returned
5	By using `basicAuth` method, you populate the `Authorization` header with user-id:password pairs, encoded using Base64.
6	The Micronaut `HttpClient` simplifies parsing the HTTP response payload to Java objects. In this example, we parse the response to `String`.
7	Use `.body()` to retrieve the parsed payload.

Use the Micronaut HTTP Client and Basic Auth

If you want to access a secured endpoint, you can also use a Micronaut HTTP Client and supply the Basic Auth as the Authorization header value.

First create a @Client with a method home which accepts an Authorization HTTP header.

kotlin/src/test/kotlin/example/micronaut/AppClient.kt

package example.micronaut

import io.micronaut.http.MediaType.TEXT_PLAIN
import io.micronaut.http.annotation.Consumes
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Header
import io.micronaut.http.client.annotation.Client

@Client("/")
interface AppClient {

    @Consumes(TEXT_PLAIN) // 
    @Get
    fun home(@Header authorization: String): String // 
}

1	The method consumes plain text, so the Micronaut framework includes the HTTP header `Accept: text/plain`.
2	The first character of the parameter name is capitalized and that value (`Authorization`) is used as the HTTP header name. To change the parameter name, specify the `@Header` annotation value.

Create a test which uses the previous @Client

kotlin/src/test/kotlin/example/micronaut/BasicAuthClientTest.kt

package example.micronaut

import io.micronaut.test.extensions.junit5.annotation.MicronautTest
import jakarta.inject.Inject
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Test
import java.util.Base64

@MicronautTest // 
class BasicAuthClientTest {

    @Inject
    lateinit var appClient : AppClient // 

    @Test
    fun verifyBasicAuthWorks() {
        val credsEncoded = Base64.getEncoder().encodeToString("sherlock:password".toByteArray())
        val rsp = appClient.home("Basic $credsEncoded") // 
        assertEquals("sherlock", rsp)
    }
}

1	Annotate the class with `@MicronautTest` so the Micronaut framework will initialize the application context and the embedded server. More info.
2	Inject the `AppClient` bean.
3	Generate Basic Auth header value and pass it as the parameter value.

Testing the Application

To run the tests:

./gradlew test

Then open build/reports/tests/test/index.html in a browser to see the results.

Running the Application

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

To test the running application, issue a GET request to localhost:8080 with a Basic Authentication header. One way to do this is with curl:

curl -v -u sherlock:password localhost:8080

If you open http://localhost:8080 in a browser, a login dialog pops up due to the WWW-Authenticate header.

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.

Note	Only Java and Kotlin projects support using GraalVM’s `native-image` tool. Groovy relies heavily on reflection, which is only partially supported by GraalVM.

GraalVM Installation

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

Java 25

sdk install java 25.0.2-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 25

sdk install java 25.0.2-graalce

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') // 
            buildArgs.add('-Ob') // 
        }
    }
}

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.

You can invoke the controller exposed by the native executable:

curl "http://localhost:8080" -u 'sherlock:password'

Next Steps

See the Micronaut security documentation to learn more.

Help with the Micronaut Framework

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

License

Note	All guides are released with an Apache License 2.0 for the code and a Creative Commons Attribution 4.0 license for the writing and media (images).