该IAM用户可以通过 $ {AWS：用户名}被称为在政策文件中。

The IAM user can be referred to in policy documents by ${aws:username}.

还有其他的IAM政策变量列表，在这里它们的用途：

There is a list of other IAM policy variables and their uses here:

http://docs.aws.amazon.com/IAM/最新/ UserGuide / PolicyVariables.html