Bug & Possible Fix: Can't login on some systems

When deploying to wpengine.com, I found I couldn’t log in as super admin if my site was down, even though it had worked fine on my dev box. I had also discovered a case of where your could trick a the plugin to show a page by hacking the url. I think the following might be a good update for in the ‘shutdown’ function:

//jjr better login detection -begin-
        # Motivation:
        # 1) handle case of wp-admin/page=update.php?ILoveHacking&blah=wp-login.php
        # 2) On standard wpengine.com multi-site install, could not login as site admin while in maint mode
		#if ($wpdb->blogid == 1 && $this->urlend('wp-login.php')) return; //I told you *not* to log out, but you did anyway. duh!
        global $pagenow;
        $isAtRootLogin = ($wpdb->blogid == 1 && $pagenow == 'wp-login.php');
        if ($isAtRootLogin) {
            return; //I told you *not* to log out, but you did anyway. duh!
        }
        // jjr -end-

https://www.ads-software.com/plugins/wpms-site-maintenance-mode/