Handle extra byte in ext-salt. Fixes #1606

Author: bgrainger

src/MySqlConnector/Core/ServerSession.cs

@@ -943,10 +943,15 @@ private async Task<PayloadData> SwitchAuthenticationAsync(ConnectionSettings cs,
 				payload = new([]);
 				await SendReplyAsync(payload, ioBehavior, cancellationToken).ConfigureAwait(false);
 				payload = await ReceiveReplyAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
+				var extendedSalt = payload.Span;
 
-				Span<byte> combinedData = stackalloc byte[switchRequest.Data.Length + payload.Span.Length];
+				// MariaDB 11.8.4 sends an extra 0x01 byte at the beginning of ext-salt; cf. https://mariadb.com/docs/server/reference/clientserver-protocol/1-connecting/connection#parsec-plugin
+				if (extendedSalt.Length == 21 && extendedSalt[0] == 1 && extendedSalt[1] == 'P')
+					extendedSalt = extendedSalt[1..];
+
+				Span<byte> combinedData = stackalloc byte[switchRequest.Data.Length + extendedSalt.Length];
 				switchRequest.Data.CopyTo(combinedData);
-				payload.Span.CopyTo(combinedData.Slice(switchRequest.Data.Length));
+				extendedSalt.CopyTo(combinedData.Slice(switchRequest.Data.Length));
 
 				parsecPlugin3.CreateResponseAndPasswordHash(password, combinedData, out var parsecResponse, out m_passwordHash);
 				payload = new(parsecResponse);