VaultDataBuilder.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Braintree\Gateway\Request;

use Magento\Payment\Gateway\Request\BuilderInterface;

/**
 * Vault Data Builder
 */
class VaultDataBuilder implements BuilderInterface
{
    /**
     * Additional options in request to gateway
     */
    const OPTIONS = 'options';

    /**
     * The option that determines whether the payment method associated with
     * the successful transaction should be stored in the Vault.
     */
    const STORE_IN_VAULT_ON_SUCCESS = 'storeInVaultOnSuccess';

    /**
     * @inheritdoc
     */
    public function build(array $buildSubject)
    {
        return [
            self::OPTIONS => [
                self::STORE_IN_VAULT_ON_SUCCESS => true
            ]
        ];
    }
}