/**
 * Change login page title tag content.
 *
 * @param string $login_title The page title, with extra context added.
 * @param string $title       The original page title.
 *
 * @return string Modified login title string.
 */
function wpdocs_login_title( $login_title, $title ) {
	$login_title = $title . ' ‹ ' . get_bloginfo( 'name' ) . '— Powered by WordPress';
	return $login_title;
}

add_filter( 'login_title', 'wpdocs_login_title' ), 10, 2 );