Accessing Keycloak-Service inside Docker by its Network Alias - docker

Question

Scenario
I have secured webservice (JakartaEE + Microprofile + JWT) running in open liberty. As issuer of the jwt token I use keycloak. For testing and development i want to run both services in docker. Therefore I wrote a docker-compose file. As test client I use JUnit with microprofile-client. This is running outside of docker.
Problem
I can retrieve the JWT-Token via localhost at the host - e.g.:
POST /auth/realms/DC/protocol/openid-connect/token HTTP/1.1
Host: localhost:8080
Content-Type: application/x-www-form-urlencoded
realm=DC&grant_type=password&client_id=dc&username=dc_editor&password=******
The problem is, that from the perspective of the webservice localhost isn't the keycloak server. The JWT-Token-Validation against the issuer fails.
Goal
I want to access the keycloak server from the host with its docker-internal network alias - e.g. dcAuthServer. The JWT-Token would be validated correctly.
Code
The docker-compose file looks like this:
version: "3.8"
services:
dcWebservice:
environment:
- DC_AUTH_SERVER_HOST=dcAuthServer
- DC_AUTH_SERVER_PORT=8080
- DC_AUTH_SERVER_REALM=DC
image: dc_webservice:latest
ports:
- "9080:9080"
networks:
- dcNetwork
dcAuthServer:
image: dc_keycloak:latest
ports:
- "8080:8080"
networks:
dcNetwork:
aliases:
- dcAuthServer
healthcheck:
test: "curl --fail http://localhost:8080/auth/realms/DC || false"
networks:
dcNetwork:
The environment DC_AUTH* are used in the mpJwt-configuration in server.xml of the open liberty server:
<mpJwt id="dcMPJWT" audiences="dc" issuer="http://${DC_AUTH_SERVER_HOST}:${DC_AUTH_SERVER_PORT}/auth/realms/${DC_AUTH_SERVER_REALM}"
jwksUri="http://${DC_AUTH_SERVER_HOST}:${DC_AUTH_SERVER_PORT}/auth/realms/${DC_AUTH_SERVER_REALM}/protocol/openid-connect/certs"/>
The issuer is where I have to put a trusted issuer for the JWT-Token.
I hope I did not forget important information - just ask!
Thanks in advance
Robert