Feature: #83529 - Execute hooks on backend user login

Description

When a user successfully logs in to the backend of TYPO3, registered hooks are executed. Developers can register their hooks as shown below.

// Register hook on successful BE user login
$GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['t3lib/class.t3lib_userauthgroup.php']['backendUserLogin'][] =
    \Vendor\MyExtension\Hooks\BackendUserLogin::class . '->dispatch';

On user login, method dispatch() of class \Vendor\MyExtension\Hooks\BackendUserLogin is executed and the backend user array is passed as a parameter:

public function dispatch(array $backendUser)
{
  if (isset($backendUser['user']['username'])) {
    $username = $backendUser['user']['username'];
    $email = $backendUser['user']['email'];
    // do something...
  }
}

Impact

TYPO3 core developers as well as extension developers can develop functions which will be executed when a backend user successfully logs in to the backend of TYPO3. A typical use case would be any type of notification service.