Fix caching_sha2_password auth over Unix domain sockets (#1757) (#1759)

MySQL treats Unix domain socket connections as secure, expecting clear-text password exchange during full authentication.

The client only checked `isSsl()` in `AuthenticationMySQLCommandBase`, falling back to RSA key exchange which MySQL 8.4.13+ no longer accepts over secure connections (Bug #39883040).

Added `isUsingDomainSocket()` to `MySQLSocketConnection` to check the actual socket transport, so clear-text passwords are sent over domain sockets, consistent with SSL connections.


(cherry picked from commit 58117cc)

Signed-off-by: Thomas Segismont <tsegismont@gmail.com>

Author: tsegismont

vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/MySQLSocketConnection.java

@@ -131,6 +131,10 @@ private void clearCachedStatements() {
     }
   }
 
+  public boolean isUsingDomainSocket() {
+    return socket.remoteAddress().isDomainSocket();
+  }
+
   @Override
   public String system() {
     return metaData.system();

vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/codec/AuthenticationCommandBaseCodec.java

@@ -47,7 +47,7 @@ protected final void handleAuthMoreData(byte[] password, ByteBuf payload) {
     } else {
       byte flag = payload.readByte();
       if (flag == FULL_AUTHENTICATION_STATUS_FLAG) {
-        if (encoder.socketConnection.isSsl()) {
+        if (encoder.socketConnection.isSsl() || encoder.socketConnection.isUsingDomainSocket()) {
           // send the non-scrambled password directly since it's on a secure connection
           int nonScrambledPasswordPacketLength = password.length + 1;
           ByteBuf nonScrambledPasswordPacket = allocateBuffer(nonScrambledPasswordPacketLength + 4);