$username = Input::json('username');
$password = Input::json('password');

$page = Input::get('page');

$client = Client::find(2);

$http = new GuzzleHttpClient();

try {
    $response = $http->post(url('oauth/token'), [   # <-- see the problem?
        'form_params' => [
            'grant_type'    => 'password',
            'client_id'     => '2',
            'client_secret' => $client->secret,
            'username'      => $username,
            'password'      => $password,
            'scope'         => '',
        ],
    ]);

#...