Firebase rest with guzzle

FirebaseService.php

<?php namespace App\Services;

use GuzzleHttp\Client;
use GuzzleHttp\Exception\ClientException;

/**
 * Class FirebaseService
 * @package App\Services
 */
class FirebaseService
{

    /**
     * Register a user in the firebase authentication
     * @param string $email
     * @param string $password
     * @return string
     */
    public function signUp(string $email, string $password)
    {
        $data['email'] = $email;
        $data['password'] = $password;
        $response = $this->execute('https://www.googleapis.com/identitytoolkit/v3/relyingparty/signupNewUser', $data);
        return $response;
    }

    /**
     * @param string $email
     * @param string $password
     * @return string
     */
    public function signIn(string $email, string $password)
    {
        $data['email'] = $email;
        $data['password'] = $password;
        $response = $this->execute('https://www.googleapis.com/identitytoolkit/v3/relyingparty/verifyPassword', $data);
        return $response;
    }

    /**
     * @param $url
     * @param array $data
     * @return null|string
     */
    private function execute($url, array $data)
    {
        $client = new  Client();
        $query['query']['key'] = env('FIREBASE_API_KEY');
        $query['json'] = $data;
        try {
            $res = $client->post($url, $query);
            if ($res->getStatusCode() == 200) {
                $response = $res->getBody()->getContents();
                return \GuzzleHttp\json_decode($response, true);
            }
        } catch (ClientException $ce) {
            logger($ce);
        } catch (\Exception $e) {
            logger($e);
        }

        return null;
    }
}