How to use GuzzleHTTP 6.1

guzzlehttp_example.php

<?php

// in a method...

        $this->client = new GuzzleHttp\Client(['base_uri' => 'my_base_uri']);
        $config = [
            'auth' => [$this->username, $this->password],
            'headers' => [
                'x-app-id' => $this->appId,
            ],
            'json' => [
                // boomtrain's id. If left blank it will search by email then
                // app_member_id
                'bsin' => '',
                'email' => $userData['email'],
                'app_member_id' => $userData['id'],
                'firstName' => $userData['first_name'],
                'lastName' => $userData['last_name'],
                'attributes' => $this->getAttributes($userData),
            ],
        ];
        return $this->client->put('persons', $config);