Magento 2.1.1 login to backend programatically, from frontend:

autologin.php

<?php

use Magento\Framework\App\Bootstrap;

require __DIR__ . '/app/bootstrap.php';

class TestApp extends \Magento\Framework\App\Http implements \Magento\Framework\AppInterface {

    public function launch() {
        $areaCode = 'adminhtml';
        $username = 'reseller';

        $this->_request->setPathInfo('/admin_ves');
        $this->_state->setAreaCode($areaCode);
        $this->_objectManager->configure($this->_configLoader->load($areaCode));

        /** @var \Magento\User\Model\User $user */
        $user = $this->_objectManager->get('Magento\User\Model\User')->loadByUsername($username);

        /** @var \Magento\Backend\Model\Auth\Session $session */
        $session = $this->_objectManager->get('Magento\Backend\Model\Auth\Session');
        $session->setUser($user);
        $session->processLogin();

        if ($session->isLoggedIn()) {
            $cookieManager = $this->_objectManager->get('Magento\Framework\Stdlib\CookieManagerInterface');
            $cookieValue = $session->getSessionId();
            if ($cookieValue) {
                $sessionConfig = $this->_objectManager->get('Magento\Backend\Model\Session\AdminConfig');
                $cookiePath = str_replace('autologin.php', 'index.php', $sessionConfig->getCookiePath());
                $cookieMetadata = $this->_objectManager->get('Magento\Framework\Stdlib\Cookie\CookieMetadataFactory')
                        ->createPublicCookieMetadata()
                        ->setDuration(3600)
                        ->setPath($cookiePath)
                        ->setDomain($sessionConfig->getCookieDomain())
                        ->setSecure($sessionConfig->getCookieSecure())
                        ->setHttpOnly($sessionConfig->getCookieHttpOnly());
                $cookieManager->setPublicCookie($session->getName(), $cookieValue, $cookieMetadata);
               $adminSessionManager = $this->_objectManager->get('Magento\Security\Model\AdminSessionsManager'); 
                $adminSessionManager->processLogin(); 
            }

            /** @var \Magento\Backend\Model\UrlInterface $backendUrl */
            $backendUrl = $this->_objectManager->get('Magento\Backend\Model\UrlInterface');
            $path = $backendUrl->getStartupPageUrl();
            $url = $backendUrl->getUrl($path);
            $url = str_replace('autologin.php', 'index.php', $url);
            header('Location:  ' . $url);
            exit;
        }
        return $this->_response;
    }

}

$bootstrap = Bootstrap::create(BP, $_SERVER);
$bootstrap = \Magento\Framework\App\Bootstrap::create(BP, $_SERVER);
/** @var \Magento\Framework\App\Http $app */
$app = $bootstrap->createApplication('TestApp');
$bootstrap->run($app);