Laravel 11 CORS problem on localhost with SvelteKit

To answer your question, I'd first like to clarify that as of now, Laravel 11 does not exist, as Laravel 8 is the latest stable release. I assume you meant Laravel 8 or a newer version.

Now, let's address the issue you're encountering with Cross-Origin Resource Sharing (CORS) between Laravel and SvelteKit on localhost.

CORS is a security feature that prevents web applications from making requests to a different domain unless the server explicitly allows it. In your case, you're trying to make requests from your SvelteKit application running on localhost to your Laravel backend also running on localhost. Since they are on the same origin, you might think CORS shouldn't be an issue. However, Laravel's default CORS configuration only allows requests from specific domains, not localhost.

To resolve this issue, follow these steps:

Install Laravel's CORS package: If you haven't already, install the Laravel CORS package using Composer:
```
composer require laravel/sanctum
composer require laravel/cors
```
Make sure to add the following lines to your composer.json file:
```
"autoload": {
    "psr-4": {
        "App\\": "app/",
        "Laravel\\": "laravel/"
    }
},
"require": {
    "laravel/cors": "^3.0"
}
```
Run composer install to install the packages.
Configure Laravel's CORS: Open your config/app.php file and add the following line to the providers array:
```
'providers' => [
    // ...
    Laravel\Cors\ServiceProvider::class,
],
```
Next, open your config/cors.php file and update the $allowedOrigins array to include localhost:
```
'allowedOrigins' => [
    '*', // Allow all origins for local development
],
```
Be aware that allowing all origins can pose a security risk. For production, you should restrict the allowed origins to trusted domains.
Update Laravel's middleware: Open your app/Http/Kernel.php file and add the following line to the $routeMiddleware array:
```
'cors' => \Laravel\Cors\HandleCors::class,
```
Next, add the following line to the $middlewareGroups array:
```
'web' => [
    // ...
    \Laravel\Cors\HandleCors::class,
],
```
Configure SvelteKit: In your SvelteKit project, open the svelte.config.js file and add the following line to the kit.config.js object:
```
cors: {
    url: 'http://localhost:8000', // Replace with your Laravel backend URL
    allowCredentials: true,
},
```
Test the setup: Now, you should be able to make requests from your SvelteKit application to your Laravel backend without encountering CORS issues. To test it, you can create an API route in Laravel and make a request from SvelteKit to that route.

For example, in Laravel, create a new route in routes/api.php:
```
Route::get('/test', function () {
    return response()->json(['message' => 'Hello from Laravel!']);
});
```
In your SvelteKit application, create a new file src/api/test.js and add the following code:
```
import fetch from 'isomorphic-unfetch';

export async function getServerSideProps() {
    const res = await fetch('http://localhost:8000/api/test');
    const data = await res.json();

    return { props: { data } };
}

export default function TestPage({ data }) {
    return <div>{JSON.stringify(data)}</div>;
}
```
This code makes a request to the Laravel route you created and returns the response as a prop to the TestPage component.

Finally, create a new page src/pages/test.svelte and import the TestPage component:
```
<script lang="ts">
    import TestPage from '$lib/api/test';

    export let { data };
</script>

<TestPage {data} />
```
Run your SvelteKit application and visit the /test page in your browser. You should see the response from Laravel displayed on the page.

That's it! You've successfully set up CORS between your Laravel backend and SvelteKit application on localhost. Remember to remove the * from the $allowedOrigins array in your config/cors.php file when you're ready to deploy your Laravel application to a production environment.