Login without authentication problem solved

It’a a pity that the plugin author is not responding to questions.

If you logout from Google and WordPress, you can still login to wordpress without authenticating for 1 hour with this plugin.
To prevent this, add this to your functions.php in your theme folder. It just clears the plugin login cookie.

add_action( 'wp_logout', 'my_nextend_logout'); 
function my_nextend_logout() {
	setcookie("nextend_uniqid","",time()-42000);
}