Ways to set different security permissions for SSAS from SSRS?

I have an SSAS cube with limited users. I don't want to grant any sort of access to the cube outside of those users.

I have some SSRS reports that use the above SSAS cube as a data source. I want to give access to the reports to some users who don't have access to the cube.

What credentials should I use for the cube data source? Since SSAS only supports Windows Authentication, do I have to create a dummy Windows ID?

Edit: Both SSAS and S开发者_如何学编程SRS are 2008.

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Usually I use a windows account that is reserved solely as a SSRS service account to control connecting SSRS to SSAS. Then I control access to the cube through permissions in SSRS. I once saw someone use a local machine account since the server doubled as the SSRS and SSAS server, but I personally prefer to secure solely through domain accounts.