secure information in environmentVariables section

hey team,

I try to put some secure access key in env for third party api call.
In the document, I think [EnvironmentVariables](https://github.com/aliyun/fun/blob/master/docs/specs/2018-04-03-zh-cn.md?spm=a2c4e.11153940.blogcont672623.24.216d4bbeUuxz1H#%E7%8E%AF%E5%A2%83%E5%8F%98%E9%87%8F%E5%AF%B9%E8%B1%A1) is something can achieve this.

But I don't want to hard code env in yml file, would like to know if there is any way to secure env in EnvironmentVariables section? For example, those secure key is in my build machine env, when I run `fun deploy` can those value be extracted from my build machine env and pass to aliyun provider?