better way to normalise base64 string

Author: ckritzinger

packages/powersync/lib/src/connector.dart

@@ -113,12 +113,8 @@ class PowerSyncCredentials {
     try {
       List<String> parts = token.split('.');
       if (parts.length == 3) {
-        String part = parts[1];
         // dart:convert doesn't like missing padding
-        if (part.length % 4 > 0) {
-          part += '=' * (4 - part.length % 4);
-        }
-        final rawData = base64Decode(part);
+        final rawData = base64Url.decode(base64.normalize(parts[1]));
         final text = Utf8Decoder().convert(rawData);
         Map<String, dynamic> payload = jsonDecode(text);
         if (payload.containsKey('exp') && payload['exp'] is int) {