login_init action-hook . WP 3.2.0

Fires when the login form is initialized.

Usage

add_action( 'login_init', 'action_function_name_3625' );
function action_function_name_3625(){
	// action...
}

Where the hook is called

do_action( 'login_init' );

Where in WP core the hook is used WordPress

add_action( 'login_init', 'wp_admin_headers' );

add_action( 'login_init', 'send_frame_options_header', 10, 0 );