code: protected List<String> defineAttributesToRead() {
          final List<String> names = new ArrayList<>();
          names.add(getIdAttribute());
          names.add(LINKEDID);
          // legacy mode: 'getIdAttribute()' + linkedid + username + attributes
          if (isLegacyMode()) {
              names.add(getUsernameAttribute());
              names.addAll(Arrays.asList(attributeNames));
          } else {
              // new beahviour (>= v2.0): 'getIdAttribute()' + linkedid + serializedprofile
              names.add(SERIALIZED_PROFILE);
          }
          return names;
      }
docs: Define the attributes to read in the storage.
  
  @return the attributes