WordPress at a glance
filter is not described

login_title filter-hook . WP 4.9.0

Filters the title tag content for login page.

Usage

add_filter( 'login_title', 'filter_function_name_2399', 10, 2 );
function filter_function_name_2399( $login_title, $title ){
	// filter...

	return $login_title;
}
$login_title(string)
The page title, with extra context added.
$title(string)
The original page title.

Where the hook is called

login_header()
wp-login.php 72
$login_title = apply_filters( 'login_title', $login_title, $title );

Where the hook is used (in WP core)

Does not used.