Enforce that Maven/Ivy repositories use https (elastic#41812)

This commit adds a check when a repository is added that we are using
https instead of http.

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -39,6 +39,8 @@ import org.gradle.api.artifacts.ModuleVersionIdentifier
 import org.gradle.api.artifacts.ProjectDependency
 import org.gradle.api.artifacts.ResolvedArtifact
 import org.gradle.api.artifacts.dsl.RepositoryHandler
+import org.gradle.api.artifacts.repositories.IvyArtifactRepository
+import org.gradle.api.artifacts.repositories.MavenArtifactRepository
 import org.gradle.api.credentials.HttpHeaderCredentials
 import org.gradle.api.execution.TaskActionListener
 import org.gradle.api.execution.TaskExecutionGraph
@@ -580,6 +582,16 @@ class BuildPlugin implements Plugin<Project> {
 
     /** Adds repositories used by ES dependencies */
     static void configureRepositories(Project project) {
+        project.getRepositories().all { repository ->
+            if (repository instanceof MavenArtifactRepository) {
+                final MavenArtifactRepository maven = (MavenArtifactRepository) repository
+                assertRepositoryURIUsesHttps(project, maven.getUrl())
+                repository.getArtifactUrls().each { uri -> assertRepositoryURIUsesHttps(project, uri) }
+            } else if (repository instanceof IvyArtifactRepository) {
+                final IvyArtifactRepository ivy = (IvyArtifactRepository) repository
+                assertRepositoryURIUsesHttps(project, ivy.getUrl())
+            }
+        }
         RepositoryHandler repos = project.repositories
         if (System.getProperty("repos.mavenLocal") != null) {
             // with -Drepos.mavenLocal=true we can force checking the local .m2 repo which is
@@ -617,6 +629,12 @@ class BuildPlugin implements Plugin<Project> {
         }
     }
 
+    private static void assertRepositoryURIUsesHttps(final Project project, final URI uri) {
+        if (uri != null && uri.toURL().getProtocol().equals("http")) {
+            throw new GradleException("repository on project with path [${project.path}] is using http for artifacts on [${uri.toURL()}]")
+        }
+    }
+
     /**
      * Returns a closure which can be used with a MavenPom for fixing problems with gradle generated poms.
      *