Micronaut Token Propagation

Learn how to leverage token propagation in the Micronaut framework to simplify your code while keeping your microservices secure.

Authors: Sergio del Amo

Micronaut Version: 3.9.2

1. Getting Started

Let’s describe the microservices you will build through the guide.

gateway - A microservice secured via JWT which exposes an endpoint /user. The output of that endpoint is the result of consuming the userecho endpoint.
userecho - A microservice secured via JWT which exposes an endpoint /user which responds with the username of the authenticated user.

The next diagram illustrates the flow:

We generate a valid JWT in the gateway microservice. Then every microservice in our application is able to validate this JWT. We want every internal request to contain a valid JWT token. If we want to talk to another microservice we need to propagate the valid JWT get received.

Setup IntelliJ IDEA to develop Micronaut Applications.

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.

Download and unzip the source

4. Writing the Application

We will write the application first without token propagation. Then we will configure token propagation, and you will see how much code we can remove.

4.1. Gateway

Create the microservice:

mn create-app example.micronaut.gateway --build=gradle --lang=groovy

Add the security-jwt module to the configuration:

build.gradle

compileOnly("io.micronaut.security:micronaut-security-annotations")
implementation("io.micronaut.security:micronaut-security-jwt")

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

intermediate-gateway/src/main/groovy/example/micronaut/AuthenticationProviderUserPassword.groovy

package example.micronaut


import io.micronaut.core.annotation.Nullable
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 implements AuthenticationProvider { (2)

    @Override
    Publisher<AuthenticationResponse> authenticate(@Nullable HttpRequest<?> httpRequest,
                                                   AuthenticationRequest<?, ?> authenticationRequest) {
        return Flux.create(emitter -> {
            if ((authenticationRequest.identity == 'sherlock' || authenticationRequest.identity == 'watson') &&
                    authenticationRequest.secret == 'password') {
                emitter.next(AuthenticationResponse.success((String) authenticationRequest.identity))
                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`.

Create a class UserController which exposes /user endpoint.

intermediate-gateway/src/main/groovy/example/micronaut/UserController.groovy

package example.micronaut

import groovy.transform.CompileStatic
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Header
import io.micronaut.http.annotation.Produces
import io.micronaut.security.annotation.Secured
import reactor.core.publisher.Mono

import static io.micronaut.http.MediaType.TEXT_PLAIN
import static io.micronaut.security.rules.SecurityRule.IS_AUTHENTICATED

@CompileStatic
@Controller('/user') (1)
class UserController {

    private final UsernameFetcher usernameFetcher

    UserController(UsernameFetcher usernameFetcher) {  (2)
        this.usernameFetcher = usernameFetcher
    }

    @Secured(IS_AUTHENTICATED)  (3)
    @Produces(TEXT_PLAIN) (4)
    @Get(5)
    Mono<String> index(@Header('Authorization') String authorization) {  (6)
        return usernameFetcher.findUsername(authorization)
    }
}

1	Annotate with `io.micronaut.http.annotation.Controller` to designate the class as a Micronaut controller.
2	Constructor dependency injection
3	Annotate with `io.micronaut.security.Secured` to configure secured access. The `isAuthenticated()` expression will allow access only to authenticated users.
4	Since we return a string which is not valid JSON, set the media type to `text/plain`.
5	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.
6	You can bind an HTTP header to a controller method argument.

Create an interface to encapsulate the collaboration with the userecho microservice.

intermediate-gateway/src/main/groovy/example/micronaut/UsernameFetcher.groovy

package example.micronaut

import io.micronaut.http.annotation.Header
import reactor.core.publisher.Mono

interface UsernameFetcher {
    Mono<String> findUsername(@Header('Authorization') String authorization)
}

Create a Micronaut HTTP Declarative client:

intermediate-gateway/src/main/groovy/example/micronaut/UserEchoClient.groovy

package example.micronaut

import io.micronaut.context.annotation.Requires
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
import reactor.core.publisher.Mono

import static io.micronaut.context.env.Environment.TEST
import static io.micronaut.http.MediaType.TEXT_PLAIN

@Client(id = 'userecho') (1)
@Requires(notEnv = TEST) (2)
interface UserEchoClient extends UsernameFetcher {

    @Override
    @Consumes(TEXT_PLAIN)
    @Get('/user') (3)
    Mono<String> findUsername(@Header('Authorization') String authorization) (4)
}

1	The `@Client` annotation is used with a service id. We will reference the exact service id in the configuration shortly.
2	Don’t load this bean in the `test` environment.
3	Use `@Get` annotation to define the client mapping
4	Supply the JWT to the HTTP Authorization header value to the `@Client` method.

Add this snippet to application.yml to configure the service URL of the echo service

intermediate-gateway/src/main/resources/application.yml

micronaut:
  http:
    services:
      userecho: (1)
        urls:
          - "http://localhost:8081" (2)

1	This is the same service ID we used in the `@Client` annotation.
2	Configure a URL where the `userecho` microservice resides.

Add this snippet to application.yml to configure security:

intermediate-gateway/src/main/resources/application.yml

micronaut:
  security:
    authentication: bearer (1)
    token:
      jwt:
        signatures:
          secret:
            generator: (2)
              secret: '"${JWT_GENERATOR_SIGNATURE_SECRET:pleaseChangeThisSecretForANewOne}"' (3)

1	Set `authentication` to `bearer` to receive a JSON response from the login endpoint.
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)

4.1.1. Tests

Provide a UsernameFetcher bean replacement for the Test environment.

intermediate-gateway/src/test/groovy/example/micronaut/UserEchoClientReplacement.groovy

package example.micronaut

import groovy.transform.CompileStatic
import io.micronaut.context.annotation.Requires
import io.micronaut.http.annotation.Header
import jakarta.inject.Singleton
import reactor.core.publisher.Mono

import static io.micronaut.context.env.Environment.TEST

@CompileStatic
@Requires(env = TEST)
@Singleton
class UserEchoClientReplacement implements UsernameFetcher {

    @Override
    Mono<String> findUsername(@Header('Authorization') String authorization) {
        return Mono.just('sherlock')
    }
}

Create tests to verify the application is secured and we can access it after login:

intermediate-gateway/src/test/groovy/example/micronaut/UserControllerSpec.groovy

package example.micronaut

import io.micronaut.http.HttpRequest
import io.micronaut.http.client.HttpClient
import io.micronaut.http.client.annotation.Client
import io.micronaut.http.client.exceptions.HttpClientResponseException
import io.micronaut.security.authentication.UsernamePasswordCredentials
import io.micronaut.security.token.jwt.render.BearerAccessRefreshToken
import io.micronaut.test.extensions.spock.annotation.MicronautTest
import jakarta.inject.Inject
import spock.lang.Specification

import static io.micronaut.http.HttpStatus.UNAUTHORIZED

@MicronautTest (1)
class UserControllerSpec extends Specification {

    @Inject
    @Client('/')
    HttpClient client (2)

    void testUserEndpointIsSecured() { (3)
        when:
        client.toBlocking().exchange(HttpRequest.GET('/user'))

        then:
        HttpClientResponseException e = thrown()
        UNAUTHORIZED == e.response.status
    }

    void testAuthenticatedCanFetchUsername() {
        when:
        UsernamePasswordCredentials credentials = new UsernamePasswordCredentials('sherlock', 'password')
        HttpRequest<?> request = HttpRequest.POST('/login', credentials)

        BearerAccessRefreshToken bearerAccessRefreshToken = client.toBlocking().retrieve(request, BearerAccessRefreshToken)

        String username = client.toBlocking().retrieve(HttpRequest.GET('/user')
                .header('Authorization', 'Bearer ' + bearerAccessRefreshToken.getAccessToken()), String)

        then:
        'sherlock' == username
    }
}

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	Test endpoint is secured

4.2. User echo

Create the microservice:

mn create-app example.micronaut.userecho --build=gradle --lang=groovy

Add the security-jwt module to the configuration:

build.gradle

compileOnly("io.micronaut.security:micronaut-security-annotations")
implementation("io.micronaut.security:micronaut-security-jwt")

Create a class UserController which exposes /user endpoint.

intermediate-userecho/src/main/groovy/example/micronaut/UserController.groovy

package example.micronaut

import groovy.transform.CompileStatic
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 java.security.Principal

import static io.micronaut.http.MediaType.TEXT_PLAIN
import static io.micronaut.security.rules.SecurityRule.IS_AUTHENTICATED

@CompileStatic
@Controller('/user') (1)
class UserController {

    @Secured(IS_AUTHENTICATED) (2)
    @Produces(TEXT_PLAIN) (3)
    @Get(4)
    String index(Principal principal) { (5)
        return principal.name
    }
}

1	Annotate with `io.micronaut.http.annotation.Controller` to designate the class as a Micronaut controller.
2	Annotate with `io.micronaut.security.Secured` to configure secured access. The `isAuthenticated()` expression will allow access only to authenticated users.
3	Since we return a string which is not valid JSON, set the media type to `text/plain`.
4	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.
5	If a user is authenticated, the Micronaut framework will bind the user object to an argument of type `java.security.Principal` (if present).

Add this snippet to application.yml to change the port where userecho starts:

intermediate-userecho/src/main/resources/application.yml

micronaut:
  server:
    port: 8081 (1)

1	Configure the port where the application listens.

Add this snippet to application.yml

intermediate-userecho/src/main/resources/application.yml

micronaut:
  security:
    token:
      jwt:
        signatures:
          secret:
            validation: (1)
              secret: '"${JWT_GENERATOR_SIGNATURE_SECRET:pleaseChangeThisSecretForANewOne}"' (2)

1	You can create a `SecretSignatureConfiguration` named `validation` which is able to validate JWT generated by the `gateway` microservice.
2	Change this to your own secret and keep it safe (do not store this in your VCS)

4.3. Token Propagation

As you can see, propagating the JWT token to other microservices in our application complicates the code. We need to capture the Authorization header in the controller method arguments and then pass it to the @Client bean. In an application with several controllers and declarative clients, it can lead to a lot of repetition. Fortunately, the Framework includes a feature called token propagation. We can tell our application to propagate the incoming token to a set of outgoing requests.

Let’s configure token propagation. We need to modify application.yml in the gateway microservice:

gateway/src/main/resources/application.yml

micronaut:
  security:
    token:
      propagation:
        enabled: true (1)
        service-id-regex: "userecho" (2)

1	Enable token propagation
2	We only want to propagate the token to certain services. We can create a regular expression to match those services ids.

We can simplify the code:

Edit UserController.java and remove the @Header parameter:

gateway/src/main/groovy/example/micronaut/UserController.groovy

package example.micronaut

import groovy.transform.CompileStatic
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 reactor.core.publisher.Mono

import static io.micronaut.http.MediaType.TEXT_PLAIN
import static io.micronaut.security.rules.SecurityRule.IS_AUTHENTICATED

@CompileStatic
@Controller('/user')
class UserController {

    private final UsernameFetcher usernameFetcher

    UserController(UsernameFetcher usernameFetcher) {
        this.usernameFetcher = usernameFetcher
    }

    @Secured(IS_AUTHENTICATED)
    @Produces(TEXT_PLAIN)
    @Get
    Mono<String> index() {
        return usernameFetcher.findUsername()
    }
}

Edit UsernameFetcher.java and remove the @Header parameter:

gateway/src/main/groovy/example/micronaut/UsernameFetcher.groovy

package example.micronaut

import reactor.core.publisher.Mono

interface UsernameFetcher {
    Mono<String> findUsername()
}

Edit UserEchoClient.java and remove the @Header parameter:

gateway/src/main/groovy/example/micronaut/UserEchoClient.groovy

package example.micronaut

import io.micronaut.context.annotation.Requires
import io.micronaut.http.annotation.Consumes
import io.micronaut.http.annotation.Get
import io.micronaut.http.client.annotation.Client
import reactor.core.publisher.Mono

import static io.micronaut.context.env.Environment.TEST
import static io.micronaut.http.MediaType.TEXT_PLAIN

@Client(id = 'userecho')
@Requires(notEnv = TEST)
interface UserEchoClient extends UsernameFetcher {

    @Consumes(TEXT_PLAIN)
    @Get('/user')
    Mono<String> findUsername()
}

Edit UserEchoClientReplacement.java and remove the @Header parameter:

gateway/src/test/groovy/example/micronaut/UserEchoClientReplacement.groovy

package example.micronaut

import groovy.transform.CompileStatic
import io.micronaut.context.annotation.Requires
import jakarta.inject.Singleton
import reactor.core.publisher.Mono

import static io.micronaut.context.env.Environment.TEST

@CompileStatic
@Requires(env = TEST)
@Singleton
class UserEchoClientReplacement implements UsernameFetcher {

    @Override
    Mono<String> findUsername() {
        return Mono.just('sherlock')
    }
}

5. Running the App

Run both microservices:

userecho

./gradlew run

18:29:26.500 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 671ms. Server Running: http://localhost:8081

gateway

./gradlew run

18:28:35.723 [main] INFO  io.micronaut.runtime.Micronaut - Startup completed in 707ms. Server Running: http://localhost:8080

Send a curl request to authenticate:

curl -X "POST" "http://localhost:8080/login" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -d $'{"username": "sherlock", "password": "password"}'

{"username":"sherlock","access_token":"eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJzaGVybG9jayIsIm5iZiI6MTYxNTkxMDM3Nywicm9sZXMiOltdLCJpc3MiOiJnYXRld2F5IiwiZXhwIjoxNjE1OTEzOTc3LCJpYXQiOjE2MTU5MTAzNzd9.nWoaNq9YzRzYKDBvDw_QaiUyVyIoc6rHCW_vLfnrtQ8","token_type":"Bearer","expires_in":3600}

Now you can call the /user endpoint supplying the access token in the Authorization header.

curl "http://localhost:8080/user" -H 'Authorization: Bearer eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJzaGVybG9jayIsIm5iZiI6MTYxNTkxMDM3Nywicm9sZXMiOltdLCJpc3MiOiJnYXRld2F5IiwiZXhwIjoxNjE1OTEzOTc3LCJpYXQiOjE2MTU5MTAzNzd9.nWoaNq9YzRzYKDBvDw_QaiUyVyIoc6rHCW_vLfnrtQ8'

sherlock

6. Next steps

Read more about Token Propagation and Micronaut Security.

7. Help with the Micronaut Framework

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

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