Get Stores, Countries, and Languages via REST API in Magento 2

Currently, my Magento version is 2.1.5, I cannot find the API for the "sign out" function. However, seem that Magento builds the revoked token by customer id method already.

vendor/magento/module-integration/Api/CustomerTokenServiceInterface.php

vendor/magento/module-integration/Model/CustomerTokenService.php::revokeCustomerAccessToken()

[NOT TEST MY CODE]

app/code/Vendor/Integration/etc/webapi.xml

<?xml version="1.0"?>

<routes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Webapi:etc/webapi.xsd">
    <route url="/V1/integration/customer/revoke" method="POST">
        <service class="Vendor\Integration\Api\CustomerRevokeTokenServiceInterface"
                 method="revokeCustomerAccessToken"/>
        <resources>
            <resource ref="anonymous"/>
        </resources>
    </route>
</routes>

app/code/Vendor/Integration/etc/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Vendor\Integration\Api\CustomerRevokeTokenServiceInterface"
                type="Vendor\Integration\Model\CustomerRevokeTokenService" />
</config>

app/code/Vendor/Integration/Api/CustomerRevokeTokenServiceInterface.php

<?php

namespace Vendor\Integration\Api;
/**
 * Interface CustomerRevokeTokenServiceInterface
 * @package Vendor\Integration\Api
 */
interface  CustomerRevokeTokenServiceInterface 
{
    /**
     * Revoke token by customer id.
     *
     * @api
     * @param int $customerId
     * @return bool
     * @throws \Magento\Framework\Exception\LocalizedException
     */
    public function revokeCustomerAccessToken($customerId);
}

app/code/Vendor/Integration/Model/CustomerRevokeTokenService.php

<?php

namespace Vendor\Integration\Model;

use Magento\Customer\Api\AccountManagementInterface;
use Magento\Framework\Exception\LocalizedException;
use Magento\Integration\Model\CredentialsValidator;
use Magento\Integration\Model\Oauth\Token as Token;
use Magento\Integration\Model\Oauth\TokenFactory as TokenModelFactory;
use Magento\Integration\Model\ResourceModel\Oauth\Token\CollectionFactory as TokenCollectionFactory;
use Magento\Integration\Model\Oauth\Token\RequestThrottler;
use Magento\Framework\Exception\AuthenticationException;

class CustomerRevokeTokenService
    implements \Vendor\Integration\Api\CustomerRevokeTokenServiceInterface
{
    /**
     * Token Model
     *
     * @var TokenModelFactory
     */
    private $tokenModelFactory;

    /**
     * Customer Account Service
     *
     * @var AccountManagementInterface
     */
    private $accountManagement;

    /**
     * @var \Magento\Integration\Model\CredentialsValidator
     */
    private $validatorHelper;

    /**
     * Token Collection Factory
     *
     * @var TokenCollectionFactory
     */
    private $tokenModelCollectionFactory;

    /**
     * @var RequestThrottler
     */
    private $requestThrottler;

    /**
     * Initialize service
     *
     * @param TokenModelFactory $tokenModelFactory
     * @param AccountManagementInterface $accountManagement
     * @param TokenCollectionFactory $tokenModelCollectionFactory
     * @param \Magento\Integration\Model\CredentialsValidator $validatorHelper
     */
    public function __construct(
        TokenModelFactory $tokenModelFactory,
        AccountManagementInterface $accountManagement,
        TokenCollectionFactory $tokenModelCollectionFactory,
        CredentialsValidator $validatorHelper
    ) {
        $this->tokenModelFactory = $tokenModelFactory;
        $this->accountManagement = $accountManagement;
        $this->tokenModelCollectionFactory = $tokenModelCollectionFactory;
        $this->validatorHelper = $validatorHelper;
    }

    /**
     * {@inheritdoc}
     */
    public function revokeCustomerAccessToken($customerId)
    {
        $tokenCollection = $this->tokenModelCollectionFactory->create()->addFilterByCustomerId($customerId);
        if ($tokenCollection->getSize() == 0) {
            throw new LocalizedException(__('This customer has no tokens.'));
        }
        try {
            foreach ($tokenCollection as $token) {
                $token->setRevoked(1)->save();
            }
        } catch (\Exception $e) {
            throw new LocalizedException(__('The tokens could not be revoked.'));
        }
        return true;
    }

}

Remember to create registration.php and module.xml files.

We can use the revoke customer access token: /V1/integration/customer/revoke

That is correct, are you sure you're using a valid category ID? Example:

https://domain.com/rest/V1/categories/2

Then you can get the sub categories from the response, response.children.