code: protected void populateAuthenticationMetadataAttributes(final AuthenticationBuilder builder,
                                                              final AuthenticationTransaction transaction) {
          LOGGER.debug("Invoking authentication metadata populators for authentication transaction");
          val pops = getAuthenticationMetadataPopulatorsForTransaction(transaction);
          pops.forEach(populator -> transaction.getCredentials()
              .stream()
              .filter(populator::supports)
              .forEach(credential -> populator.populateAttributes(builder, transaction)));
      }
docs: Populate authentication metadata attributes.
  
  @param builder     the builder
  @param transaction the transaction