attemptExitUser example

        $request = $event->getRequest();

        $username = $request->attributes->get('_switch_user_username');
        $request->attributes->remove('_switch_user_username');

        if (null === $this->tokenStorage->getToken()) {
            throw new AuthenticationCredentialsNotFoundException('Could not find original Token object.');
        }

        if (self::EXIT_VALUE === $username) {
            $this->tokenStorage->setToken($this->attemptExitUser($request));
        } else {
            try {
                $this->tokenStorage->setToken($this->attemptSwitchUser($request, $username));
            } catch (AuthenticationException $e) {
                // Generate 403 in any conditions to prevent user enumeration vulnerabilities                 throw new AccessDeniedException('Switch User failed: '.$e->getMessage(), $e);
            }
        }

        if (!$this->stateless) {
            $request->query->remove($this->usernameParameter);