Laravel Passport

// composer create-project --prefer-dist laravel/laravel server-demo
// composer create-project --prefer-dist laravel/laravel client-demo

// cd server-demo
// php artisan serve --port 8001

// cd client-demo
// php artisan serve --port 8000

// client-demo --> resource server
// server-demo --> authorize server

Route::get('/redirect', function () {

    $query = http_build_query([
        'client_id' => '3',
        'redirect_uri' => 'http://127.0.0.1:8000/callback',
        'response_type' => 'code',
        'scope' => ''
    ]);

    return redirect('http://127.0.0.1:8001/oauth/authorize?'.$query);
});

Route::get('/callback', function (Illuminate\Http\Request $request) {
    $http = new \GuzzleHttp\Client;

    $response = $http->post('http://127.0.0.1:8001/oauth/token', [
        'form_params' => [
            'client_id' => '3',
            'client_secret' => 'fdFaiBUBjDmLoKiBmFpuTvLyAXyoCuusAvJljBQF',
            'grant_type' => 'authorization_code',
            'redirect_uri' => 'http://127.0.0.1:8000/callback',
            'code' => $request->code,
        ],
    ]);
    return json_decode((string) $response->getBody(), true);
});