[ARTEMIS-1597] validate non null callback principal for login success

artemis-server/src/main/java/org/apache/activemq/artemis/spi/core/security/jaas/Krb5LoginModule.java

@@ -58,12 +58,15 @@ public class Krb5LoginModule implements LoginModule {
       callbacks[0] = new Krb5Callback();
       try {
          callbackHandler.handle(callbacks);
+         Principal principal = ((Krb5Callback)callbacks[0]).getPeerPrincipal();
+         if (principal != null) {
+            principals.add(principal);
+         }
       } catch (IOException ioe) {
          throw new LoginException(ioe.getMessage());
       } catch (UnsupportedCallbackException uce) {
          throw new LoginException(uce.getMessage() + " not available to obtain information from user");
       }
-      principals.add(((Krb5Callback)callbacks[0]).getPeerPrincipal());
       if (!principals.isEmpty()) {
          loginSucceeded = true;
       }

artemis-server/src/test/java/org/apache/activemq/artemis/spi/core/security/jaas/Krb5LoginModuleTest.java

@@ -0,0 +1,62 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.activemq.artemis.spi.core.security.jaas;
+
+import org.junit.Test;
+
+import javax.security.auth.Subject;
+import javax.security.auth.callback.Callback;
+import javax.security.auth.callback.CallbackHandler;
+import javax.security.auth.callback.UnsupportedCallbackException;
+
+import java.io.IOException;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class Krb5LoginModuleTest {
+
+   @Test
+   public void loginFail() throws Exception {
+      Krb5LoginModule underTest = new Krb5LoginModule();
+
+      final Subject subject = new Subject();
+      underTest.initialize(subject, new CallbackHandler() {
+         @Override
+         public void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException {
+         }
+      }, null, null);
+
+      assertFalse(underTest.login());
+   }
+
+   @Test
+   public void loginSuccess() throws Exception {
+      Krb5LoginModule underTest = new Krb5LoginModule();
+
+      final Subject subject = new Subject();
+      underTest.initialize(subject, new CallbackHandler() {
+         @Override
+         public void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException {
+            ((Krb5Callback) callbacks[0]).setPeerPrincipal(new UserPrincipal("A"));
+         }
+      }, null, null);
+
+      assertTrue(underTest.login());
+   }
+
+}