install barryvdh/laravel-cors package code example

Example: laravel 5.8 cors

Create a simple middleware called Cors:
php artisan make:middleware Cors
  
Add the following code to app/Http/Middleware/Cors.php:

public function handle($request, Closure $next)
{
    return $next($request)
        ->header('Access-Control-Allow-Origin', '*')
        ->header('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS')
        ->header('Access-Control-Allow-Headers', 'Origin, Content-Type, Accept, Authorization, X-Request-With');
}
You can replace the * with localhost or keep it as it is.

Next step is to load the middleware. Add the following line to the $routeMiddleware array in app/Http/Kernel.php.

'cors' => \App\Http\Middleware\Cors::class, 
And the final step is to use the middleware on the routes to which you want to set the access origin headers. Assuming you are talking about the new api routes in laravel 5.3, the place to do it is app/Providers/RouteServiceProvider.php, inside the mapApiRoutes() function (you can remove or comment the previous code of the function):

    Route::group([
        'middleware' => ['api', 'cors'],
        'namespace' => $this->namespace,
        'prefix' => 'api',
    ], function ($router) {
         //Add you routes here, for example:
         Route::apiResource('/posts','PostController');
    });