Regenerate session id on login to avoid session fixation attacks

AI-assistant: Copilot v1.0.7 (Claude Opus 4.6)

Signed-off-by: Pablo Zmdl <pablo@nextcloud.com>

php/src/Auth/AuthManager.php

@@ -26,6 +26,7 @@ readonly class AuthManager {
     public function SetAuthState(bool $isLoggedIn) : void {
 
         if (!$this->IsAuthenticated() && $isLoggedIn === true) {
+            session_regenerate_id(true);
             $date = new DateTime();
             $dateTime = $date->getTimestamp();
             $_SESSION['date_time'] = $dateTime;