feat: add maven verification plugin

internal/builders/maven/plugins/verification-plugin/README.md

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+# Maven verification plugin
+
+The Maven verification plugin can be used to verify the provenance of the dependencies of a Java project.
+
+It is meant to make it easy for project owners and consumers to:
+1: Check how many and which dependencies of a Maven-based project are released with provenance files.
+2: Verify the provenance files of the dependencies of a given Maven-based project.
+
+The plugin wraps the [the slsa verifier](https://github.com/slsa-framework/slsa-verifier) and invokes it for all the dependencies in a `pom.xml`.
+
+## Prerequisites
+
+To use the plugin you must have Go, Java and Maven installed. It has currently only been tested on Ubuntu.
+
+The plugin requires that the slsa-verifier is already installed on the machine.
+
+## Development status
+
+The plugin is in its early stages and is not ready for production.
+
+Things that work well are:
+1: Resolving dependencies and checking whether they have provenance files in the remote repository.
+2: Running the slsa-verifier against dependencies with provenance files.
+3: Outputting the result from the slsa-verifier.
+
+Things that are unfinished:
+1: What to do with the results from the verifier. Currently we have not taken a stand on what the Maven verification plugin should do with the output from the slsa-verifier. This is a UX decision more than it is a technical decision.
+
+## Using the Maven verification plugin
+
+### Invoking it directly
+
+It can be run from the root of a given project file.
+A pseudo-workflow looks like this:
+  1: `git clone --depth=1 https://github.com/slsa-framework/slsa-github-generator`
+  2: `cd slsa-github-generator/internal/builders/maven/plugins/verification-plugin`
+  3: `mvn clean install`
+  4: `cd /tmp`
+  5: `git clone your repository to text`
+  6: `cd into your repository`
+  7: `mvn io.github.adamkorcz:slsa-verification-plugin:0.0.1:verify`
+
+The plugin will now go through all the dependencies in the `pom.xml` file and check if they have a provenance statement attached to their release. If a dependency has a SLSA provenance file, the Maven verification plugin will fetch it from the remote repository and invoke the `slsa-verifier` binary against the dependency and the provenance file.
+
+### Integrating it into your Maven build cycle
+
+The plugin can also live in your Maven build cycle. If you add it to your own `pom.xml`, the plugin will execute during the validation phase of the Maven build cycle.

internal/builders/maven/plugins/verification-plugin/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>io.github.adamkorcz</groupId>
+    <artifactId>slsa-verification-plugin</artifactId>
+    <packaging>maven-plugin</packaging>
+    <version>0.0.1</version>
+
+    <name>Slsa Verification Mojo</name>
+    <url>http://maven.apache.org</url>
+
+    <properties>
+        <maven.compiler.target>1.8</maven.compiler.target>
+        <maven.compiler.source>1.8</maven.compiler.source>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.maven</groupId>
+            <artifactId>maven-core</artifactId>
+            <version>3.2.5</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven</groupId>
+            <artifactId>maven-plugin-api</artifactId>
+            <version>3.6.3</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven.plugin-tools</groupId>
+            <artifactId>maven-plugin-annotations</artifactId>
+            <version>3.6.0</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven</groupId>
+            <artifactId>maven-project</artifactId>
+            <version>2.2.1</version>
+        </dependency>
+        <dependency>
+            <groupId>org.twdata.maven</groupId>
+            <artifactId>mojo-executor</artifactId>
+            <version>2.4.0</version>
+        </dependency>
+    </dependencies>
+</project>

internal/builders/maven/plugins/verification-plugin/src/main/java/io/github/adamkorcz/SlsaVerificationMojo.java

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+// Copyright 2023 SLSA Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package io.github.adamkorcz;
+
+import org.apache.maven.artifact.Artifact;
+import org.apache.maven.execution.MavenSession;
+import org.apache.maven.plugin.AbstractMojo;
+import org.apache.maven.plugin.BuildPluginManager;
+import org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugin.MojoFailureException;
+import org.apache.maven.plugins.annotations.LifecyclePhase;
+import org.apache.maven.plugins.annotations.Component;
+import org.apache.maven.plugins.annotations.Mojo;
+import org.apache.maven.plugins.annotations.Parameter;
+import org.apache.maven.project.MavenProject;
+
+import static org.twdata.maven.mojoexecutor.MojoExecutor.*;
+
+import java.io.File;
+import java.util.Set;
+
+/*
+ SlsaVerificationMojo is a Maven plugin that wraps https://github.com/slsa-framework/slsa-verifier.
+ At a high level, it does the following:
+   1: Install the slsa-verifier.
+   2: Loop through all dependencies of a pom.xml. Resolve each dependency.
+   3: Check if each dependency also has a provenance file.
+   4: Run the slsa-verifier for the dependency if there is a provenance file.
+   5: Output the results.
+
+ The plugin is meant to be installed and then run from the root of a given project file.
+ A pseudo-workflow looks like this:
+   1: git clone --depth=1 https://github.com/slsa-framework/slsa-github-generator
+   2: cd slsa-github-generator/internal/builders/maven/plugins/verification-plugin
+   3: mvn clean install
+   4: cd /tmp
+   5: git clone your repository
+   6: cd into your repository
+   7: mvn io.github.adamkorcz:slsa-verification-plugin:0.0.1:verify
+*/
+@Mojo(name = "verify", defaultPhase = LifecyclePhase.VALIDATE)
+public class SlsaVerificationMojo extends AbstractMojo {
+    @Parameter(defaultValue = "${project}", required = true, readonly = true)
+    private MavenProject project;
+
+    /**
+      * Custom path of GOHOME, default value is $HOME/go
+    **/
+    @Parameter(property = "slsa.verifier.path", required = true)
+    private String verifierPath;
+
+    @Component
+    private MavenSession mavenSession;
+
+    @Component
+    private BuildPluginManager pluginManager;
+
+
+    public void execute() throws MojoExecutionException, MojoFailureException {
+        // Verify the slsa of each dependency
+        Set<Artifact> dependencyArtifacts = project.getDependencyArtifacts();
+        for (Artifact artifact : dependencyArtifacts ) {
+            // Retrieve the dependency jar and its slsa file
+            String artifactStr = artifact.getGroupId() + ":" + artifact.getArtifactId() + ":" + artifact.getVersion();
+            try {
+                // Retrieve the slsa file of the artifact
+                executeMojo(
+                    plugin(
+                        groupId("com.googlecode.maven-download-plugin"),
+                        artifactId("download-maven-plugin"),
+                        version("1.7.0")
+                    ),
+                    goal("artifact"),
+                    configuration(
+                        element(name("outputDirectory"), "${project.build.directory}/slsa"),
+                        element(name("groupId"), artifact.getGroupId()),
+                        element(name("artifactId"), artifact.getArtifactId()),
+                        element(name("version"), artifact.getVersion()),
+                        element(name("type"), "intoto.build.slsa"),
+                        element(name("classifier"), "jar")
+                    ),
+                    executionEnvironment(
+                        project,
+                        mavenSession,
+                        pluginManager
+                    )
+                );
+
+                // Retrieve the dependency jar if slsa file does exists for this artifact
+                executeMojo(
+                    plugin(
+                        groupId("org.apache.maven.plugins"),
+                        artifactId("maven-dependency-plugin"),
+                        version("3.6.0")
+                    ),
+                    goal("copy"),
+                    configuration(
+                        element(name("outputDirectory"), "${project.build.directory}/slsa"),
+                        element(name("artifact"), artifactStr)
+                    ),
+                    executionEnvironment(
+                        project,
+                        mavenSession,
+                        pluginManager
+                    )
+                );
+            } catch(MojoExecutionException e) {
+                getLog().info("Skipping slsa verification for " + artifactStr + ": No slsa file found.");
+                continue;
+            }
+
+            // Verify slsa file
+            try {
+                // Run slsa verification on the artifact and print the result
+                // It will never fail the build process
+                // This might be prone to command-injections. TODO: Secure against that. 
+                String arguments = "verify-artifact --provenance-path ";
+                arguments += "${project.build.directory}/slsa/" + artifact.getArtifactId() + "-" + artifact.getVersion() + "-jar.intoto.build.slsa ";
+                arguments += " --source-uri ./ ${project.build.directory}/slsa/" + artifact.getArtifactId() + "-" + artifact.getVersion() + ".jar";
+                executeMojo(
+                    plugin(
+                        groupId("org.codehaus.mojo"),
+                        artifactId("exec-maven-plugin"),
+                        version("3.1.0")
+                    ),
+                    goal("exec"),
+                    configuration(
+                        element(name("executable"), verifierPath),
+                        element(name("commandlineArgs"), arguments),
+                        element(name("useMavenLogger"), "true")
+                    ),
+                    executionEnvironment(
+                        project,
+                        mavenSession,
+                        pluginManager
+                    )
+                );
+            } catch(MojoExecutionException e) {
+                // TODO: Properly interpret the output based on the verification plugin.
+                getLog().info("Skipping slsa verification: Fail to run slsa verifier.");
+                return;
+            }
+        }
+    }
+}