Hash password for generating client id for mqtt clients

Fixes #2653

smallrye-reactive-messaging-mqtt/src/main/java/io/smallrye/reactive/messaging/mqtt/Clients.java

@@ -2,6 +2,10 @@
 
 import static io.smallrye.reactive.messaging.mqtt.i18n.MqttLogging.log;
 
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
@@ -21,16 +25,44 @@ private Clients() {
         // avoid direct instantiation.
     }
 
+    private static String sha512(String password) {
+        if (password == null || password.isEmpty()) {
+            return null;
+        }
+        MessageDigest messageDigest = getMessageDigest("SHA-512");
+        SecureRandom random = new SecureRandom();
+        byte[] salt = new byte[16];
+        random.nextBytes(salt);
+        messageDigest.update(salt);
+        StringBuilder sb = new StringBuilder();
+        toHex(messageDigest.digest(password.getBytes(StandardCharsets.UTF_8)), sb);
+        return sb.toString();
+    }
+
+    private static void toHex(byte[] digest, StringBuilder sb) {
+        for (byte b : digest) {
+            sb.append(Integer.toHexString((b & 0xFF) | 0x100), 1, 3);
+        }
+    }
+
+    private static MessageDigest getMessageDigest(String alg) {
+        try {
+            return MessageDigest.getInstance(alg);
+        } catch (NoSuchAlgorithmException e) {
+            throw new IllegalArgumentException(e);
+        }
+    }
+
     static ClientHolder getHolder(Vertx vertx, MqttClientSessionOptions options) {
 
         String host = options.getHostname();
         int port = options.getPort();
         String clientId = options.getClientId();
         String server = options.getServerName().orElse(null);
         String username = options.getUsername();
-        String password = options.getPassword();
+        String pwdDigest = sha512(options.getPassword());
 
-        String id = username + ":" + password + "@"
+        String id = username + ":" + pwdDigest + "@"
                 + host + ":"
                 + port
                 + "<" + (server == null ? "" : server)