PHP框架的扩展机制如何应用于实际项目中？

namespace App\Providers;

use Illuminate\Support\ServiceProvider;

class CustomAuthProviderServiceProvider extends ServiceProvider
{
    /**
     * Register services.
     *
     * @return void
     */
    public function register()
    {
        $this->app->singleton('auth.driver.custom', function () {
            return new CustomAuthProvider();
        });
    }
}

'providers' => [
    // 其他服务提供者
    App\Providers\CustomAuthProviderServiceProvider::class,
]

namespace App\Auth;

use Illuminate\Auth\GuardHelpers;
use Illuminate\Contracts\Auth\Guard;
use Illuminate\Contracts\Auth\UserProvider;
use Illuminate\Contracts\Auth\Authenticatable;

class CustomAuthProvider implements Guard
{
    use GuardHelpers;

    /**
     * Create a new guard instance.
     *
     * @param  \Illuminate\Contracts\Auth\UserProvider  $provider
     * @param  string $name
     * @return void
     */
    public function __construct(UserProvider $provider, $name = '')
    {
        $this->provider = $provider;
    }

    // ...其他 Guard 接口方法的实现
}

'guards' => [
    // 其他守卫
    'custom' => [
        'driver' => 'custom',
        'provider' => 'users',
    ]
]

Auth::guard('custom')->attempt(['username' => 'username', 'password' => 'password']);