WordPress at a glance
action is not described

auth_cookie_valid action-hook . WP 2.7.0

Fires once an authentication cookie has been validated.

Usage

add_action( 'auth_cookie_valid', 'action_function_name_9954', 10, 2 );
function action_function_name_9954( $cookie_elements, $user ){
	// action...
}
$cookie_elements(array)
An array of data for the authentication cookie.
$user(WP_User)
User object.

Where the hook is called

wp_validate_auth_cookie()
auth_cookie_valid
wp-includes/pluggable.php 686
do_action( 'auth_cookie_valid', $cookie_elements, $user );

Where the hook is used (in WP core)

wp-includes/default-filters.php 264
add_action( 'auth_cookie_valid', 'rest_cookie_collect_status' );