Session based authentication

Learn how to secure a Micronaut application using Session based authentication.

Authors: Sergio del Amo

Micronaut Version: 3.7.0

1. Getting Started

In this guide, we will create a Micronaut application written in Kotlin with session based authentication.

The following sequence illustrates the authentication flow:

session based auth

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-session,views-velocity,reactor,graalvm example.micronaut.micronautguide --build=gradle --lang=kotlin --test=spock
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-session, views-velocity, 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. Configuration

Add this configuration to application.yml:

src/main/resources/application.yml
micronaut:
  security:
    authentication: session (1)
    redirect:
      login-success: / (2)
      login-failure: /login/authFailed (3)
1 Set micronaut.security.authentication to session. It sets the necessary beans for login and logout using session based authentication.
2 After the user logs in, redirect them to the Home page.
3 If the login fails, redirect them to /login/authFailed

4.3. Authentication Provider

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

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

import io.micronaut.http.HttpRequest
import io.micronaut.security.authentication.AuthenticationProvider
import io.micronaut.security.authentication.AuthenticationRequest
import io.micronaut.security.authentication.AuthenticationResponse
import jakarta.inject.Singleton
import org.reactivestreams.Publisher
import reactor.core.publisher.Flux
import reactor.core.publisher.FluxSink

@Singleton (1)
class AuthenticationProviderUserPassword : AuthenticationProvider { (2)
    override fun authenticate(httpRequest: HttpRequest<*>?,
                              authenticationRequest: AuthenticationRequest<*, *>): Publisher<AuthenticationResponse> {
        return Flux.create({ emitter: FluxSink<AuthenticationResponse> ->
            if (authenticationRequest.identity == "sherlock" && authenticationRequest.secret == "password") {
                emitter.next(AuthenticationResponse.success(authenticationRequest.identity as String))
                emitter.complete()
            } else {
                emitter.error(AuthenticationResponse.exception())
            }
        }, FluxSink.OverflowStrategy.ERROR)
    }
}
1 Use jakarta.inject.Singleton to designate a class as a singleton.
2 A Micronaut Authentication Provider implements the interface io.micronaut.security.authentication.AuthenticationProvider.

4.4. Apache Velocity

By default, Micronaut controllers produce JSON. Usually, you consume those endpoints with a mobile phone application, or a JavaScript front end (Angular, React, Vue.js, etc.). However, to keep this guide simple we will produce HTML in our controllers.

In order to do that, we use Apache Velocity and the Micronaut Server Side View Rendering Module.

Velocity is a Java-based template engine. It permits anyone to use a simple yet powerful template language to reference objects defined in Java code.

Create two velocity templates in src/main/resources/views:

src/main/resources/views/home.vm
<!DOCTYPE html>
<html>
    <head>
        <title>Home</title>
    </head>
    <body>
        #if( $loggedIn )
            <h1>username: <span>$username</span></h1>
        #else
            <h1>You are not logged in</h1>
        #end
        #if( $loggedIn )
            <form action="logout" method="POST">
                <input type="submit" value="Logout"/>
            </form>
        #else
            <p><a href="/login/auth">Login</a></p>
        #end
    </body>
</html>
src/main/resources/views/auth.vm
<!DOCTYPE html>
<html>
    <head>
        #if( $errors )
            <title>Login Failed</title>
        #else
            <title>Login</title>
        #end
    </head>
<body>
    <form action="/login" method="POST">
        <ol>
            <li>
                <label for="username">Username</label>
                <input type="text" name="username" id="username"/>
            </li>
            <li>
                <label for="password">Password</label>
                <input type="password" name="password" id="password"/>
            </li>
            <li>
                <input type="submit" value="Login"/>
            </li>
            #if( $errors )
                <li id="errors">
                    <span style="color: red;">Login Failed</span>
                </li>
            #end
        </ol>
    </form>
</body>
</html>

4.5. Controllers

Create HomeController which resolves the base URL /:

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
import java.security.Principal

@Secured(SecurityRule.IS_ANONYMOUS) (1)
@Controller (2)
class HomeController {

    @Get (3)
    @View("home") (4)
    fun index(principal: Principal?): Map<String, Any> { (5)
        val data = mutableMapOf<String, Any>("loggedIn" to (principal != null))
        if (principal != null) {
            data["username"] = principal.name
        }
        return data
    }
}
1 Annotate with io.micronaut.security.Secured to configure security access. Use isAnonymous() expression to allow access to authenticated and unauthenticated 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 io.micronaut.http.annotation.Get
4 Use View annotation to specify which template to use to render the response.
5 If you are authenticated, you can use the java.security.Principal as a parameter type. For parameters which may be null, use io.micronaut.core.annotation.Nullable.

5. Login Form

Next, create LoginAuthController which renders the login form.

src/main/kotlin/example/micronaut/LoginAuthController.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

@Secured(SecurityRule.IS_ANONYMOUS) (1)
@Controller("/login") (2)
class LoginAuthController {

    @Get("/auth") (3)
    @View("auth") (4)
    fun auth(): Map<String, Any> = mutableMapOf()

    @Get("/authFailed") (5)
    @View("auth") (4)
    fun authFailed(): Map<String, Any> = mutableMapOf("errors" to true)
}
1 Annotate with io.micronaut.security.Secured to configure security access. Use isAnonymous() expression for anonymous access.
2 Annotate with io.micronaut.http.annotation.Controller to designate the class as a Micronaut controller.
3 Responds to GET requests at /login/auth
4 Use View annotation to specify which template to use to render the response.
5 Responds to GET requests at /login/authFailed

6. Tests

We also use Geb, a browser automation solution.

To use Geb, add these dependencies:

build.gradle
testImplementation("org.gebish:geb-spock:5.1")
testImplementation("org.seleniumhq.selenium:htmlunit-driver:3.62.0")
testRuntimeOnly("org.seleniumhq.selenium:selenium-chrome-driver:4.3.0")

Geb uses the Page concept pattern; the Page Object Pattern gives us a common sense way to model content in a reusable and maintainable way.

Create three pages:

src/test/groovy/example/micronaut/HomePage.groovy
package example.micronaut

import geb.Page

class HomePage extends Page {

    static url = '/'

    static at = { title == 'Home' }

    static content = {
        loginLink { $('a', text: 'Login') }
        logoutButton { $('input', type: 'submit', value: 'Logout') }
        usernameElement(required: false) { $('h1 span', 0) }
    }

    String username() {
        usernameElement.empty ? null : usernameElement.text()
    }

    void login() {
        loginLink.click()
    }

    void logout() {
        logoutButton.click()
    }
}
src/test/groovy/example/micronaut/LoginPage.groovy
package example.micronaut

import geb.Page

class LoginPage extends Page {

    static url = '/login/auth'

    static at = { title.contains 'Login' }

    static content = {
        usernameInput { $('#username') }
        passwordInput { $('#password') }
        submitInput { $('input', type: 'submit') }
        errorsLi(required: false) { $('li#errors') }
    }

    boolean hasErrors() {
        !errorsLi.empty
    }

    void login(String username, String password) {
        usernameInput = username
        passwordInput = password
        submitInput.click()
    }
}
src/test/groovy/example/micronaut/LoginFailedPage.groovy
package example.micronaut

import geb.Page

class LoginFailedPage extends Page {

    static at = { title == 'Login Failed' }

    static url = '/login/authFailed'
}

Create a test to verify the user authentication flow.

src/test/groovy/example/micronaut/SessionAuthenticationSpec.groovy
package example.micronaut

import geb.spock.GebSpec
import io.micronaut.runtime.server.EmbeddedServer
import io.micronaut.test.extensions.spock.annotation.MicronautTest
import jakarta.inject.Inject

@MicronautTest (1)
class SessionAuthenticationSpec extends GebSpec {

    @Inject
    EmbeddedServer embeddedServer (2)

    def "verify session based authentication works"() {
        given:
        browser.baseUrl = "http://localhost:${embeddedServer.port}"

        when:
        to HomePage

        then:
        at HomePage

        when:
        HomePage homePage = browser.page HomePage

        then: 'As we are not logged in, there is no username'
        homePage.username() == null

        when: 'click the login link'
        homePage.login()

        then:
        at LoginPage

        when: 'fill the login form, with invalid credentials'
        LoginPage loginPage = browser.page LoginPage
        loginPage.login('foo', 'foo')

        then: 'the user is still in the login form'
        at LoginPage

        and: 'and error is displayed'
        loginPage.hasErrors()

        when: 'fill the form with wrong credentials'
        loginPage.login('sherlock', 'foo')

        then: 'we get redirected to the home page'
        at LoginFailedPage

        when: 'fill the form with valid credentials'
        loginPage.login('sherlock', 'password')

        then: 'we get redirected to the home page'
        at HomePage

        when:
        homePage = browser.page HomePage

        then: 'the username is populated'
        homePage.username() == 'sherlock'

        when: 'click the logout button'
        homePage.logout()

        then: 'we are in the home page'
        at HomePage

        when:
        homePage = browser.page HomePage

        then: 'but we are no longer logged in'
        homePage.username() == null
    }
}
1 Annotate the class with @MicronautTest so the Micronaut framework will initialize the application context and the embedded server. More info.
2 Inject the EmbeddedServer bean.

7. Testing the Application

To run the tests:

./gradlew test

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

8. Running the Application

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

9. 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.

9.1. Native executable generation

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

Java 11
sdk install java 22.1.0.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 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') (1)
            buildArgs.add('--verbose') (2)
        }
    }
}
1 The native executable name will now be mn-graalvm-application
2 It is possible to pass extra arguments to build the native executable

10. Next steps

Explore more features with Micronaut Guides.

11. Help with the Micronaut Framework

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