How laravel `Auth:user()` or `Auth:id()` works

Here's my attempt at figuring out what actually happens on an Auth::user() call:

Auth::user()

Illuminate\Support\Facades\Auth
extends Illuminate\Support\Facades\Facade

Facade::__callStatic('user')

static::getFacadeRoot()

resolveFacadeInstance(static::getFacadeAccessor == 'auth' (from Auth class))

return static::$app[$name];
static::$app is instance of Illuminate\Foundation\Application
extends Illuminate\Container\Container

which implements ArrayAccess (which is why $obj[] syntax works)

Container::offsetGet(auth)

Application::make(auth) 

Container::getAlias(auth) return 'auth'

Container::make(auth)

Container::resolve(auth)

yadda, yadda, yadda See in Application::registerCoreContainerAliases

'auth' = Illuminate\Auth\AuthManager

AuthManager::user() = AuthManager::__call = $this->guard()->user()

AuthManager::guard(web)

AuthManager::resolve(web) (see config/auth.php)

AuthManager::createSessionDriver() returns new Illuminate\Auth\SessionGuard

SessionGuard::user() // <---- this is what actually get's called, based on default config

Did you read this? Its a good guide to start with

https://laravel.com/docs/5.4/authentication