!!! THIS DOES NOT WORK !!!

EncryptedS3Adapter.php

<?php

namespace App\Adapters;

use League\Flysystem\Config;
use League\Flysystem\AwsS3V3\AwsS3V3Adapter;

class EncryptedS3Adapter extends AwsS3V3Adapter
{
    public function write(string $path, string $contents, Config $config): void
    {
        $contents = encrypt($contents);

        Parent::write($path, $contents, $config);
    }

    public function writeStream(string $path, $contents, Config $config): void
    {
        $contents = encrypt($contents);

        // TODO: this does not work

        Parent::writeStream($path, $contents, $config);
    }

    public function read(string $path): string
    {
        $contents = Parent::read($path);

        return decrypt($contents);
    }

    public function readStream(string $path)
    {
        $resource = Parent::readStream($path);

        // TODO: this also does not work

        return $resource;
    }
}

EncryptedS3Provider.php

<?php

namespace App\Providers;

use App\Adapters\EncryptedS3Adapter;
use League\Flysystem\Filesystem;
use Illuminate\Filesystem\FilesystemAdapter;
use Illuminate\Support\Facades\Storage;
use Illuminate\Support\Facades\URL;
use Illuminate\Support\ServiceProvider;

class EncryptedS3Provider extends ServiceProvider
{
    /**
     * Register services.
     *
     * @return void
     */
    public function register()
    {
        //
    }

    /**
     * Bootstrap services.
     *
     * @return void
     */
    public function boot()
    {
        Storage::extend('s3-encrypted', function ($app, $config) {
            $adapter = new EncryptedS3Adapter(
                Storage::disk('s3')->getClient(),
                $config['bucket'],
            );

            return new FilesystemAdapter(
                new Filesystem($adapter, $config),
                $adapter,
                $config
            );
        });

        Storage::disk('s3-encrypted')->buildTemporaryUrlsUsing(fn ($path) => route('file', $path));
    }
}

filesystems.php

<?php

return [

    /*
    |--------------------------------------------------------------------------
    | Default Filesystem Disk
    |--------------------------------------------------------------------------
    |
    | Here you may specify the default filesystem disk that should be used
    | by the framework. The "local" disk, as well as a variety of cloud
    | based disks are available to your application. Just store away!
    |
    */

    'default' => env('FILESYSTEM_DISK', 'local'),

    /*
    |--------------------------------------------------------------------------
    | Filesystem Disks
    |--------------------------------------------------------------------------
    |
    | Here you may configure as many filesystem "disks" as you wish, and you
    | may even configure multiple disks of the same driver. Defaults have
    | been set up for each driver as an example of the required values.
    |
    | Supported Drivers: "local", "ftp", "sftp", "s3"
    |
    */

    'disks' => [

        'local' => [
            'driver' => 'local',
            'root' => storage_path('app'),
            'throw' => false,
        ],

        'public' => [
            'driver' => 'local',
            'root' => storage_path('app/public'),
            'url' => env('APP_URL') . '/storage',
            'visibility' => 'public',
            'throw' => false,
        ],

        's3' => [
            'driver' => 's3',
            'key' => env('AWS_ACCESS_KEY_ID'),
            'secret' => env('AWS_SECRET_ACCESS_KEY'),
            'region' => env('AWS_DEFAULT_REGION'),
            'bucket' => env('AWS_BUCKET'),
            'url' => env('AWS_URL'),
            'endpoint' => env('AWS_ENDPOINT'),
            'use_path_style_endpoint' => env('AWS_USE_PATH_STYLE_ENDPOINT', false),
            'throw' => false,
        ],

        's3-encrypted' => [
            'driver' => 's3-encrypted',
            'bucket' => env('AWS_BUCKET'),
        ],
    ],

    /*
    |--------------------------------------------------------------------------
    | Symbolic Links
    |--------------------------------------------------------------------------
    |
    | Here you may configure the symbolic links that will be created when the
    | `storage:link` Artisan command is executed. The array keys should be
    | the locations of the links and the values should be their targets.
    |
    */

    'links' => [
        public_path('storage') => storage_path('app/public'),
    ],

];

This is my failed attempt to create a laravel filesystem driver that encrypts files before uploading them to S3.