[KAFKA-15117] In TestSslUtils set SubjectAlternativeNames to null if there are no hostnames (#14440)

We are currently encoding an empty hostNames array to subjectAltName in the keystore. While parsing the certificates in the test this causes the issue - Unparseable SubjectAlternativeName extension due to java.io.IOException: No data available in passed DER encoded value. Up to Java 17, this parsing error was ignored. This PR assigns subjectAltName to null if hostnames are empty.

Co-authored-by: Ismael Juma <ismael@juma.me.uk>
Reviewers: Rajini Sivaram <rajinisivaram@googlemail.com>

clients/src/test/java/org/apache/kafka/common/network/SslTransportLayerTest.java

@@ -36,8 +36,6 @@ import org.apache.kafka.common.utils.Utils;
 import org.apache.kafka.test.TestSslUtils;
 import org.apache.kafka.test.TestUtils;
 import org.junit.jupiter.api.AfterEach;
-import org.junit.jupiter.api.condition.DisabledOnJre;
-import org.junit.jupiter.api.condition.JRE;
 import org.junit.jupiter.api.extension.ExtensionContext;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
@@ -195,7 +193,6 @@ public class SslTransportLayerTest {
      */
     @ParameterizedTest
     @ArgumentsSource(SslTransportLayerArgumentsProvider.class)
-    @DisabledOnJre(value = {JRE.JAVA_20, JRE.JAVA_21}, disabledReason = "KAFKA-15117")
     public void testValidEndpointIdentificationCN(Args args) throws Exception {
         args.serverCertStores = certBuilder(true, "localhost", args.useInlinePem).build();
         args.clientCertStores = certBuilder(false, "localhost", args.useInlinePem).build();

clients/src/test/java/org/apache/kafka/test/TestSslUtils.java

@@ -399,10 +399,14 @@ public class TestSslUtils {
         }
 
         public CertificateBuilder sanDnsNames(String... hostNames) throws IOException {
-            GeneralName[] altNames = new GeneralName[hostNames.length];
-            for (int i = 0; i < hostNames.length; i++)
-                altNames[i] = new GeneralName(GeneralName.dNSName, hostNames[i]);
-            subjectAltName = GeneralNames.getInstance(new DERSequence(altNames)).getEncoded();
+            if (hostNames.length > 0) {
+                GeneralName[] altNames = new GeneralName[hostNames.length];
+                for (int i = 0; i < hostNames.length; i++)
+                    altNames[i] = new GeneralName(GeneralName.dNSName, hostNames[i]);
+                subjectAltName = GeneralNames.getInstance(new DERSequence(altNames)).getEncoded();
+            } else {
+                subjectAltName = null;
+            }
             return this;
         }