您需要更改此行:

wp_set_auth_cookie( $user, 0, 0);

对此:

wp_set_auth_cookie( $user->ID, 0, 0);

$user是WP_User对象而不是用户ID.

$user is a WP_User Object not user id.

wp_signon失败时返回WP_Error，成功则返回WP_User.

wp_signon returns WP_Error on failure, or WP_User on success.