Configure Docker host in build plugins

This commit adds the ability to configure the Maven and Gradle
plugins to use a remote Docker daemon using build file
configuration, as an alternative to setting environment variables
to specify remote host connection details.

Fixes gh-23400

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/docs/asciidoc/packaging-oci-image.adoc

@@ -57,6 +57,24 @@ The following table shows the environment variables and their values:
 
 On Linux and macOS, these environment variables can be set using the command `eval $(minikube docker-env)` after minikube has been started.
 
+Docker daemon connection information can also be provided using `docker` parameters in the plugin configuration.
+The following table summarizes the available parameters:
+
+|===
+| Parameter | Description
+
+| `host`
+| URL containing the host and port for the Docker daemon - e.g. `tcp://192.168.99.100:2376`
+
+| `tlsVerify`
+| Enable secure HTTPS protocol when set to `true` (optional)
+
+| `certPath`
+| Path to certificate and key files for HTTPS (required if `tlsVerify` is `true`, ignored otherwise)
+|===
+
+For more details, see also <<build-image-example-docker,examples>>.
+
 
 
 [[build-image-docker-registry]]
@@ -287,7 +305,31 @@ The image name can be specified on the command line as well, as shown in this ex
 
 [[build-image-example-docker]]
 ==== Docker Configuration
-If the builder or run image are stored in a private Docker registry that supports user authentication, authentication details can be provided as shown in the following example:
+If you need the plugin to communicate with the Docker daemon using a remote connection instead of the default local connection, the connection details can be provided using `docker` parameters as shown in the following example:
+
+[source,xml,indent=0,subs="verbatim,attributes"]
+----
+	<project>
+		<build>
+			<plugins>
+				<plugin>
+					<groupId>org.springframework.boot</groupId>
+					<artifactId>spring-boot-maven-plugin</artifactId>
+					<version>{gradle-project-version}</version>
+					<configuration>
+						<docker>
+							<host>tcp://192.168.99.100:2376</host>
+							<tlsVerify>true</tlsVerify>
+							<certPath>/home/user/.minikube/certs</certPath>
+						</docker>
+					</configuration>
+				</plugin>
+			</plugins>
+		</build>
+	</project>
+----
+
+If the builder or run image are stored in a private Docker registry that supports user authentication, authentication details can be provided using `docker.registry` parameters as shown in the following example:
 
 [source,xml,indent=0,subs="verbatim,attributes"]
 ----
@@ -314,7 +356,7 @@ If the builder or run image are stored in a private Docker registry that support
 	</project>
 ----
 
-If the builder or run image is stored in a private Docker registry that supports token authentication, the token value can be provided as shown in the following example:
+If the builder or run image is stored in a private Docker registry that supports token authentication, the token value can be provided using `docker.registry` parameters as shown in the following example:
 
 [source,xml,indent=0,subs="verbatim,attributes"]
 ----

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/Docker.java

@@ -27,8 +27,38 @@ import org.springframework.boot.buildpack.platform.docker.configuration.DockerCo
  */
 public class Docker {
 
+	private String host;
+
+	private boolean tlsVerify;
+
+	private String certPath;
+
 	private DockerRegistry registry;
 
+	public String getHost() {
+		return this.host;
+	}
+
+	public void setHost(String host) {
+		this.host = host;
+	}
+
+	public boolean isTlsVerify() {
+		return this.tlsVerify;
+	}
+
+	public void setTlsVerify(boolean tlsVerify) {
+		this.tlsVerify = tlsVerify;
+	}
+
+	public String getCertPath() {
+		return this.certPath;
+	}
+
+	public void setCertPath(String certPath) {
+		this.certPath = certPath;
+	}
+
 	/**
 	 * Sets the {@link DockerRegistry} that configures registry authentication.
 	 * @param registry the registry configuration
@@ -44,17 +74,30 @@ public class Docker {
 	 * @return the Docker configuration
 	 */
 	DockerConfiguration asDockerConfiguration() {
+		DockerConfiguration dockerConfiguration = new DockerConfiguration();
+		dockerConfiguration = customizeHost(dockerConfiguration);
+		dockerConfiguration = customizeAuthentication(dockerConfiguration);
+		return dockerConfiguration;
+	}
+
+	private DockerConfiguration customizeHost(DockerConfiguration dockerConfiguration) {
+		if (this.host != null) {
+			return dockerConfiguration.withHost(this.host, this.tlsVerify, this.certPath);
+		}
+		return dockerConfiguration;
+	}
+
+	private DockerConfiguration customizeAuthentication(DockerConfiguration dockerConfiguration) {
 		if (this.registry == null || this.registry.isEmpty()) {
-			return null;
+			return dockerConfiguration;
 		}
 		if (this.registry.hasTokenAuth() && !this.registry.hasUserAuth()) {
-			return DockerConfiguration.withRegistryTokenAuthentication(this.registry.getToken());
+			return dockerConfiguration.withRegistryTokenAuthentication(this.registry.getToken());
 		}
 		if (this.registry.hasUserAuth() && !this.registry.hasTokenAuth()) {
-			return DockerConfiguration.withRegistryUserAuthentication(this.registry.getUsername(),
+			return dockerConfiguration.withRegistryUserAuthentication(this.registry.getUsername(),
 					this.registry.getPassword(), this.registry.getUrl(), this.registry.getEmail());
 		}
-
 		throw new IllegalArgumentException(
 				"Invalid Docker registry configuration, either token or username/password must be provided");
 	}

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/test/java/org/springframework/boot/maven/DockerTests.java

@@ -19,6 +19,7 @@ package org.springframework.boot.maven;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.buildpack.platform.docker.configuration.DockerConfiguration;
+import org.springframework.boot.buildpack.platform.docker.configuration.DockerHost;
 import org.springframework.boot.buildpack.platform.docker.configuration.DockerRegistryAuthentication;
 import org.springframework.util.Base64Utils;
 
@@ -34,17 +35,24 @@ import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException
 public class DockerTests {
 
 	@Test
-	void asDockerConfigurationWithoutRegistry() {
+	void asDockerConfigurationWithDefaults() {
 		Docker docker = new Docker();
-		assertThat(docker.asDockerConfiguration()).isNull();
+		assertThat(docker.asDockerConfiguration().getHost()).isNull();
+		assertThat(docker.asDockerConfiguration().getRegistryAuthentication()).isNull();
 	}
 
 	@Test
-	void asDockerConfigurationWithEmptyRegistry() {
-		Docker.DockerRegistry dockerRegistry = new Docker.DockerRegistry();
+	void asDockerConfigurationWithHostConfiguration() {
 		Docker docker = new Docker();
-		docker.setRegistry(dockerRegistry);
-		assertThat(docker.asDockerConfiguration()).isNull();
+		docker.setHost("docker.example.com");
+		docker.setTlsVerify(true);
+		docker.setCertPath("/tmp/ca-cert");
+		DockerConfiguration dockerConfiguration = docker.asDockerConfiguration();
+		DockerHost host = dockerConfiguration.getHost();
+		assertThat(host.getAddress()).isEqualTo("docker.example.com");
+		assertThat(host.isSecure()).isEqualTo(true);
+		assertThat(host.getCertificatePath()).isEqualTo("/tmp/ca-cert");
+		assertThat(docker.asDockerConfiguration().getRegistryAuthentication()).isNull();
 	}
 
 	@Test