phorge-phorge/src/applications/settings/controller/PhabricatorSettingsAdjustController.php

<?php

final class PhabricatorSettingsAdjustController
  extends PhabricatorController {

  public function handleRequest(AphrontRequest $request) {
    $viewer = $this->getViewer();

    $preferences = PhabricatorUserPreferences::loadUserPreferences($viewer);

    $editor = id(new PhabricatorUserPreferencesEditor())
      ->setActor($viewer)
      ->setContentSourceFromRequest($request)
      ->setContinueOnNoEffect(true)
      ->setContinueOnMissingFields(true);

    $key = $request->getStr('key');
    $value = $request->getStr('value');

    $xactions = array();
    $xactions[] = $preferences->newTransaction($key, $value);

    $editor->applyTransactions($preferences, $xactions);

    return id(new AphrontAjaxResponse())->setContent(array());
  }
}