Implements hook_entity_field_access_alter().
\Drupal\system\Tests\Entity\FieldAccessTest::testFieldAccess()
function entity_test_entity_field_access_alter(array &$grants, array $context) {
$field = $context['field'];
if ($field
->getName() == 'field_test_text' && $field->value == 'access alter value') {
$grants[':default'] = FALSE;
}
}