Opauth.php

// extPath . Classes\Controller\AuthentificationController.php
<?php
namespace Butenko\Opauth\Controller;

use TYPO3\CMS\Core\Utility\ExtensionManagementUtility;

class AuthentificationController extends \TYPO3\CMS\Extbase\Mvc\Controller\ActionController {}
?>

// ext_tables.php
<?php
if (TYPO3_MODE === 'FE') {
	\TYPO3\CMS\Extbase\Utility\ExtensionUtility::configurePlugin(
		'Butenko.' . $_EXTKEY,
		'Auth',
		array(
			'Authentification' => 'authenticate,callback',
		),
		array(
			'Authentification' => 'authenticate,callback',
		)
	);
}
?>

// setup.txt
OpauthLoginpage = PAGE
OpauthLoginpage {
    typeNum = 21071992
    config {
        no_cache = 1
    }
    headerData >
    21071992 = USER_INT
    21071992 {
        userFunc = \TYPO3\CMS\Extbase\Core\Bootstrap->run
        extensionName = Opauth
        pluginName = Authentification
        vendorName = Butenko
    }
}

But he try to call class:Tx_Opauth_Controller_AuthentificationController