$field_list = PhabricatorCustomField::getObjectFields(
$task,
PhabricatorCustomField::ROLE_EDIT);
$field_list
->setViewer($user)
->readFieldsFromStorage($task);
foreach ($field_list as $field) {
if ($field->getFieldKey() == 'something special') {
$security_value = $field->getValue();
break;
}
}