Value in my custom base field added to user entity isn't saved

Question

I've created a new custom basefield for user entity type like this:

function hd_is_integration_entity_base_field_info_alter(&$fields, \Drupal\Core\Entity\EntityTypeInterface $entity_type) {
  if ($entity_type->id() === 'user') {
    $fields['is_uid'] = BaseFieldDefinition::create('text')
      ->setName('is_uid')
      ->setLabel(t('IS User ID'))
      ->setDescription(t('ID of this user in HD IS.'))
      ->setSettings([
        'max_length' => 50,
        'text_processing' => 0,
      ])
      ->setDefaultValue('')
      ->setDisplayOptions('view', [
        'label' => 'above',
        'type' => 'string',
        'weight' => 0,
      ])
      ->setDisplayOptions('form', [
        'type' => 'string_textfield',
        'weight' => 0,
      ])
      ->setDisplayConfigurable('form', TRUE)
      ->setDisplayConfigurable('view', TRUE);
  }
}

I've also updated the entity schema with update hook:

function hd_is_integration_update_8001(&$sandbox) {
  $field_storage_definition = BaseFieldDefinition::create('string')
    ->setName('is_uid')
    ->setLabel(t('IS User ID'))
    ->setDescription(t('ID of this user in HD IS.'))
    ->setSettings([
      'max_length' => 50,
      'text_processing' => 0,
    ])
    ->setDefaultValue('')
    ->setDisplayOptions('view', [
      'label' => 'above',
      'type' => 'string',
      'weight' => 0,
    ])
    ->setDisplayOptions('form', [
      'type' => 'string_textfield',
      'weight' => 0,
    ])
    ->setDisplayConfigurable('form', TRUE)
    ->setDisplayConfigurable('view', TRUE);

  \Drupal::entityDefinitionUpdateManager()
    ->installFieldStorageDefinition('is_uid', 'user', 'user', $field_storage_definition);
}

The field is displaying fine in the user edit form, but any value added in it isn't saved. What am I missing, please?

Answer 1

In the end, I mofified my approach using https://www.drupal.org/project/one_time_password as an example. The difference is probably in the installation of the field definition - hook_install() works just fine.