$response = $client->post('https://login.salesforce.com/services/oauth2/token', [
    'form_params' => [
        'grant_type' => 'password',
        'client_id' => env('SALESFORCE_CLIENT_ID'),
        'client_secret' => env('SALESFORCE_CLIENT_SECRET'),
        'username' => env('SALESFORCE_USERNAME'),
        'password' => env('SALESFORCE_PASSWORD') . env('SALESFORCE_SECURITY_TOKEN'),
    ],
]);