configure signature for releases

build.gradle

@@ -105,10 +105,15 @@ publishing {
 }
 
 signing {
-    sign publishing.publications.maven
+    afterEvaluate { project ->
+        required { isReleaseVersion && gradle.taskGraph.hasTask("uploadArchives") }
+        def signingKey = findProperty("signingKey")
+        def signingPassword = findProperty("signingPassword")
+        useInMemoryPgpKeys(signingKey, signingPassword)
+        sign publishing.publications.mavenJava
+    }
 }
 
-
 javadoc {
     if (JavaVersion.current().isJava9Compatible()) {
         options.addBooleanOption('html5', true)