Fail to get token fetched from keycloak using keycloak-admin-client

import org.keycloak.OAuth2Constants;
import org.keycloak.admin.client.KeycloakBuilder;
import org.keycloak.representations.AccessTokenResponse;

import javax.enterprise.context.ApplicationScoped;


@ApplicationScoped
public class GrantToken {

    public AccessTokenResponse grantToken() {
        return KeycloakBuilder.builder()
                    .serverUrl("http://localhost:8880/auth")
                    .realm("dcm4che")
                    .clientId("elasticsearch")
                    .clientSecret("9da58af0-fd1a-4a83-b9c3-71c2641f68e4")
                    .grantType(OAuth2Constants.CLIENT_CREDENTIALS)
                    .build()
                .tokenManager()
        .grantToken();
    }
}

package org.arquillian.example;

import org.jboss.arquillian.container.test.api.Deployment;
import org.jboss.arquillian.junit.Arquillian;
import org.jboss.shrinkwrap.api.Archive;
import org.jboss.shrinkwrap.api.ShrinkWrap;
import org.jboss.shrinkwrap.api.spec.WebArchive;
import org.jboss.shrinkwrap.resolver.api.maven.Maven;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.keycloak.representations.AccessTokenResponse;

import javax.inject.Inject;

@RunWith(Arquillian.class)
public class GrantTokenTest {

    @Inject
    private GrantToken grantToken;

    @Deployment
    public static Archive<?> createDeployment() {
        return ShrinkWrap.create(WebArchive.class, "test.war")
                .addClass(GrantToken.class)
                .addAsLibraries(Maven.resolver()
                        .resolve("org.keycloak:keycloak-admin-client:5.0.0")
                        .withTransitivity()
                        .asFile());
    }

    @Test
    public void grantToken() {
        AccessTokenResponse token = grantToken.grantToken();
        Assert.assertNotNull(token.getToken());
    }
}

<jboss-deployment-structure>
    <deployment>
        <exclusions>
            <module name="org.jboss.resteasy.resteasy-json-binding-provider"/>
        </exclusions>
    </deployment>
    <sub-deployment name="xxxx.war">
        <exclusions>
            <module name="org.jboss.resteasy.resteasy-json-binding-provider"/>
        </exclusions>
    </sub-deployment>
</jboss-deployment-structure>