cakephp4 ログイン認証機能

現在ネットの情報からcakephp4でログイン認証機能を作ろうと試みております。そこで
src/application.phpにて

php
1use Cake\Core\Configure;
2use Cake\Core\ContainerInterface;
3use Cake\Core\Exception\MissingPluginException;
4use Cake\Datasource\FactoryLocator;
5use Cake\Error\Middleware\ErrorHandlerMiddleware;
6use Cake\Http\BaseApplication;
7use Cake\Http\Middleware\BodyParserMiddleware;
8use Cake\Http\Middleware\CsrfProtectionMiddleware;
9use Cake\Http\MiddlewareQueue;
10use Cake\ORM\Locator\TableLocator;
11use Cake\Routing\Middleware\AssetMiddleware;
12use Cake\Routing\Middleware\RoutingMiddleware;
13use Authentication\AuthenticationService;
14use Authentication\AuthenticationServiceInterface;
15use Authentication\AuthenticationServiceProviderInterface;
16use Authentication\Middleware\AuthenticationMiddleware;
17use Cake\Routing\Router;
18use Psr\Http\Message\ServerRequestInterface;
19/**
20 * Application setup class.
21 *
22 * This defines the bootstrapping logic and middleware layers you
23 * want to use in your application.
24 */
25class Application extends BaseApplication implements AuthenticationServiceProviderInterface
26{
27    //ネットに書いてある処理
28}

このように記載したところ

Fatal error: Uncaught Error: Interface 'Authentication\AuthenticationServiceProviderInterface' not found in /var/www/html/sample/src/Application.php:43 Stack trace: #0 /var/www/html/sample/vendor/composer/ClassLoader.php(444): include() #1 /var/www/html/sample/vendor/composer/ClassLoader.php(322): Composer\Autoload\includeFile('/var/www/html/s...') #2 [internal function]: Composer\Autoload\ClassLoader->loadClass('App\Application') #3 /var/www/html/sample/webroot/index.php(37): spl_autoload_call('App\Application') #4 {main} thrown in /var/www/html/sample/src/Application.php on line 43

このようなエラーメッセージが吐かれます。

自分の考えだとエラーの原因は最初に読み込んだAuthenticationプラグインの場所が悪いからだと思い、cakephpプラジェクトのrootディレクトリについて調べたのですが、ネットで調べてもいまいちcakephpプラジェクトのrootディレクトリというのがどこにあるのか分かりません。もしよければcakephpプラジェクトのrootディレクトリというものがどこを指示しているのか。このエラーメッセージの原因は何なのか。この二点をご教授して頂きたいです。
宜しくお願い致します。

参考にしたサイト↓↓↓↓↓↓↓↓↓↓
CakePHP 4 で Authentication プラグインを使ってユーザー認証を実装
 CakePHP4でブログサイト作るチュートリアル
 CakePHP4でログイン、ログアウトを実装する
 CakePHP4を試す

composer.jsonファイル

php
1{
2    "name": "cakephp/app",
3    "description": "CakePHP skeleton app",
4    "homepage": "https://cakephp.org",
5    "type": "project",
6    "license": "MIT",
7    "require": {
8        "php": ">=7.2",
9        "cakephp/cakephp": "~4.2.0",
10        "cakephp/migrations": "^3.0",
11        "cakephp/plugin-installer": "^1.3",
12        "mobiledetect/mobiledetectlib": "^2.8"
13    },
14    "require-dev": {
15        "cakephp/bake": "^2.3",
16        "cakephp/cakephp-codesniffer": "~4.2.0",
17        "cakephp/debug_kit": "^4.4",
18        "josegonzalez/dotenv": "^3.2",
19        "phpunit/phpunit": "~8.5.0 || ^9.3",
20        "psy/psysh": "@stable"
21    },
22    "suggest": {
23        "markstory/asset_compress": "An asset compression plugin which provides file concatenation and a flexible filter system for preprocessing and minification.",
24        "dereuromark/cakephp-ide-helper": "After baking your code, this keeps your annotations in sync with the code evolving from there on for maximum IDE and PHPStan/Psalm compatibility.",
25        "phpstan/phpstan": "PHPStan focuses on finding errors in your code without actually running it. It catches whole classes of bugs even before you write tests for the code."
26    },
27    "autoload": {
28        "psr-4": {
29            "App\": "src/"
30        }
31    },
32    "autoload-dev": {
33        "psr-4": {
34            "App\Test\": "tests/",
35            "Cake\Test\": "vendor/cakephp/cakephp/tests/"
36        }
37    },
38    "scripts": {
39        "post-install-cmd": "App\Console\Installer::postInstall",
40        "post-create-project-cmd": "App\Console\Installer::postInstall",
41        "check": [
42            "@test",
43            "@cs-check"
44        ],
45        "cs-check": "phpcs --colors -p  src/ tests/",
46        "cs-fix": "phpcbf --colors -p src/ tests/",
47        "stan": "phpstan analyse",
48        "test": "phpunit --colors=always"
49    },
50    "prefer-stable": true,
51    "config": {
52        "sort-packages": true
53    }
54}