Spring Boot Maven Plugin > 2.4.x build image publish on GitLab registry

I'm currently developing a GitLab CI/CD pipeline which compiles, tests and builds a standard Spring Boot application.

I want to package it in a docker image and publish that to the GitLab registry to use it later on.

Spring Boot recently added the build-image goal to its maven plugin which also has the ability to publish the image to a registry.

My problem is, that I can't get the auth to work.

I'm using a maven:3.6.3-jdk-11-slim image for the job with the docker:dind service to have access to a docker daemon. Building the image runs fine, but publishing fails. I configured the maven plugin in the project pom to use properties for auth, which will be overwritten by the CLI in my CI/CD Job as follows:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <docker>
            <publishRegistry>
                <username>${CI_REGISTRY_USER}</username>
                <password>${CI_REGISTRY_PASSWORD}</password>
                <url>${CI_REGISTRY}</url>
            </publishRegistry>
        </docker>
    </configuration>
</plugin>

Properties defined in the POM with no value (Will be filled in by CLI call) :

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <java.version>11</java.version>
    <CI_REGISTRY/>
    <CI_REGISTRY_USER/>
    <CI_REGISTRY_PASSWORD/>
</properties>

My maven CLI call in the Pipeline/Job uses the GitLab registry variables :

docker image job:
  stage: Build
  image: maven:3.6.3-jdk-11-slim
  services:
    - docker:dind
  script:
    - echo "java.runtime.version=11" > system.properties
    - mvn spring-boot:build-image -DCI_REGISTRY=$CI_REGISTRY -DCI_REGISTRY_USER=$CI_REGISTRY_USER -DCI_REGISTRY_PASSWORD=$CI_REGISTRY_PASSWORD -Dspring-boot.build-image.imageName=SpringBootImage_${CI_JOB_ID} -Dspring-boot.build-image.publish=true

I was following the instructions via GitLab and Spring Boot documentation, but cant seem to identify my problem.

GitLab Registry Auth documentation Spring Boot Maven Plugin image publishing documentation

I know it's been a while but in case others are trying to accomplish this

This works well

<plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
  <configuration>                   
    <mainClass>com.foo.Main</mainClass>
  </configuration>
  <executions>
    <execution>
      <goals>
        <goal>build-image</goal>
      </goals>
      <phase>deploy</phase>
      <configuration>
        <image>
          <name>${env.CI_REGISTRY_IMAGE}/${project.artifactId}:${project.version} </name>
          <publish>true</publish>
        </image>
        <docker>
          <publishRegistry>
             <username>${env.CI_REGISTRY_USER}</username>
             <password>${env.CI_REGISTRY_PASSWORD}</password>
          </publishRegistry>
        </docker>
      </configuration>
    </execution>
  </executions>
</plugin>

It uses gitlab-ci built-in env vars to configure everything