Authentication against private registry fails

Description

I'm trying to push an image to a private registry using docker-maven-plugin, but it doesn't seem to work.

How to reproduce

settings.xml:

<server>
            <id>my.repo</id>
            <username>user</username>
            <password>password</password>
            <configuration>
                 <email>foo@bar.com</email>
            </configuration>
</server>

pom.xml:

<plugin>
                <groupId>com.spotify</groupId>
                <artifactId>docker-maven-plugin</artifactId>
                <version>1.0.0</version>
                <configuration>
                    <serverId>my.repo</serverId>
                    <registryUrl>https://hostname:5000/v2/</registryUrl>
                    <imageName>hostname:5000/config</imageName>
                    <baseImage>openjdk:8-jre</baseImage>
                    <entryPoint>
                        ["java", "-jar", "/${project.build.finalName}.jar", "-XX:+UnlockExperimentalVMOptions", "-XX:+UseCGroupMemoryLimitForHeap"]
                    </entryPoint>
                    <resources>
                        <resource>
                            <targetPath>/</targetPath>
                            <directory>${project.build.directory}</directory>
                            <include>${project.build.finalName}.jar</include>
                        </resource>
                    </resources>
                </configuration>
                <executions>
                    <execution>
                        <id>build-image</id>
                        <phase>install</phase>
                        <goals>
                            <goal>build</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>push-image</id>
                        <phase>deploy</phase>
                        <goals>
                            <goal>push</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

What do you expect

I expect an image to be pushed successfully upon mvn docker:push.

What happened instead

It fails with no basic auth credentials.

Software:

docker version: 18.03.0-ce, build 0520e24
docker-maven-plugin version: 1.0.0
maven version: 3.3.9

Full backtrace

[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building config 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- docker-maven-plugin:1.0.0:push (default-cli) @ config ---
[INFO] Using Google application default credentials
[INFO] loaded credentials for user account with clientId=764086051850-6qr4p6gpi6hn506pt8ejuq83di341hur.apps.googleusercontent.com
[INFO] Using authentication suppliers: [ConfigFileRegistryAuthSupplier, ContainerRegistryAuthSupplier, NoOpRegistryAuthSupplier]
[INFO] Pushing hostname:5000/config
The push refers to repository [hostname:5000/config]
ca17aa526170: Preparing 
148268bf14be: Preparing 
6a47dae912f7: Preparing 
00439e7d6354: Preparing 
a1a8b7f7efac: Preparing 
341d865c1c22: Waiting 
61c06e07759a: Waiting 
bcbe43405751: Waiting 
e1df5dc88d2c: Waiting 
[WARNING] Failed to push hostname:5000/config, retrying in 10 seconds (1/5).
[INFO] Pushing hostname:5000/config
The push refers to repository [hostname:5000/config]
ca17aa526170: Preparing 
148268bf14be: Preparing 
6a47dae912f7: Preparing 
00439e7d6354: Preparing 
a1a8b7f7efac: Preparing 
341d865c1c22: Waiting 
61c06e07759a: Waiting 
bcbe43405751: Waiting 
e1df5dc88d2c: Waiting 
[WARNING] Failed to push hostname:5000/config, retrying in 10 seconds (2/5).
[INFO] Pushing hostname:5000/config
The push refers to repository [hostname:5000/config]
ca17aa526170: Preparing 
148268bf14be: Preparing 
6a47dae912f7: Preparing 
00439e7d6354: Preparing 
a1a8b7f7efac: Preparing 
341d865c1c22: Waiting 
61c06e07759a: Waiting 
bcbe43405751: Waiting 
e1df5dc88d2c: Preparing 
[WARNING] Failed to push hostname:5000/config, retrying in 10 seconds (3/5).
[INFO] Pushing hostname:5000/config
The push refers to repository [hostname:5000/config]
ca17aa526170: Preparing 
148268bf14be: Preparing 
6a47dae912f7: Preparing 
00439e7d6354: Preparing 
a1a8b7f7efac: Preparing 
341d865c1c22: Waiting 
61c06e07759a: Waiting 
bcbe43405751: Waiting 
e1df5dc88d2c: Waiting 
[WARNING] Failed to push hostname:5000/config, retrying in 10 seconds (4/5).
[INFO] Pushing hostname:5000/config
The push refers to repository [hostname:5000/config]
ca17aa526170: Preparing 
148268bf14be: Preparing 
6a47dae912f7: Preparing 
00439e7d6354: Preparing 
a1a8b7f7efac: Preparing 
341d865c1c22: Waiting 
61c06e07759a: Waiting 
bcbe43405751: Waiting 
e1df5dc88d2c: Waiting 
[WARNING] Failed to push hostname:5000/config, retrying in 10 seconds (5/5).
[INFO] Pushing hostname:5000/config
The push refers to repository [hostname:5000/config]
ca17aa526170: Preparing 
148268bf14be: Preparing 
6a47dae912f7: Preparing 
00439e7d6354: Preparing 
a1a8b7f7efac: Preparing 
341d865c1c22: Waiting 
61c06e07759a: Waiting 
bcbe43405751: Waiting 
e1df5dc88d2c: Waiting 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 53.742 s
[INFO] Finished at: 2018-04-07T17:30:18+02:00
[INFO] Final Memory: 22M/75M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.spotify:docker-maven-plugin:1.0.0:push (default-cli) on project config: Exception caught: no basic auth credentials -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

spotify / docker-maven-plugin

Authentication against private registry fails #377