WordPress at a glance
function is not described

wp_authenticate_cookie() WP 2.8.0

Authenticate the user using the WordPress auth cookie.

  • Global. String. $auth_secure_cookie

No Hooks.

Return

WP_User/WP_Error. WP_User on success, WP_Error on failure.

Usage

wp_authenticate_cookie( $user, $username, $password );
$user(WP_User/WP_Error/null) (required)
WP_User or WP_Error object from a previous callback.
Default: null
$username(string) (required)
Username. If not empty, cancels the cookie authentication.
$password(string) (required)
Password. If not empty, cancels the cookie authentication.

Code of wp authenticate cookie: wp-includes/user.php WP 5.2.2

<?php
function wp_authenticate_cookie( $user, $username, $password ) {
	if ( $user instanceof WP_User ) {
		return $user;
	}

	if ( empty( $username ) && empty( $password ) ) {
		$user_id = wp_validate_auth_cookie();
		if ( $user_id ) {
			return new WP_User( $user_id );
		}

		global $auth_secure_cookie;

		if ( $auth_secure_cookie ) {
			$auth_cookie = SECURE_AUTH_COOKIE;
		} else {
			$auth_cookie = AUTH_COOKIE;
		}

		if ( ! empty( $_COOKIE[ $auth_cookie ] ) ) {
			return new WP_Error( 'expired_session', __( 'Please log in again.' ) );
		}

		// If the cookie is not set, be silent.
	}

	return $user;
}