class SsoSessionBlock extends BlockBase {
    /**
     * {@inheritdoc}
     */
    public function build(){
        $value = 'dav';
        $session = Drupal::service('user.private_tempstore')->get('achva_sso');
        $session->set('name', $value);


        return [
            '#type' => 'markup',
            '#markup' => $this->t('The output of super SsoSessionBlock block.'),
        ];
    }
}

<?php

namespace Drupalachva_ssoController;

use DrupalCoreControllerControllerBase;
use DrupalCoreRoutingTrustedRedirectResponse;
use Drupaluser;


class SsoController extends ControllerBase{
    public function ssoLogout(){

        $session = Drupal::service('user.private_tempstore')->get('achva_sso');
        PrivateTempStore::delete('name');

        if(isset($session)){
            $status = $session .' is logged in';
        }else{
            $status = 'is logged out';
        }
        return[
            '#type' => 'markup',
            '#markup' => '<p>' . $status . '</p>' ,
        ];



    }
}