您的原始403错误表明您错误地为您的服务设置了身份验证帐户。但是，即使您已经完成了这项工作，截至目前（2015年11月10日），无法通过服务帐户执行Apps脚本。

Your original 403 error indicates that you have incorrectly set up authentication for your service account. However, even if you get that working, as of now (10 Nov 2015) you cannot execute Apps Scripts via the Service Account.

一个已知的错误，并且正在使用应用程序脚本进行跟踪问题跟踪器。

It's a known bug, and is being tracked in the Apps Scripts Issue Tracker.