WordPress at a glance
action is not described

login_header action-hook . WP 4.6.0

Fires in the login page header after the body tag is opened.

Usage

add_action( 'login_header', 'action_function_name_4392' );
function action_function_name_4392(){
	// action...
}

Where the hook is called

login_header()
wp-login.php 182
do_action( 'login_header' );

Where the hook is used (in WP core)

Does not used.