SQL Server - sql native mode kerberos

This is standard SQL server SSRS deployment in Native mode. Created SPN a/c for a domain account on RS. & it impersonate the users to preview the reports. I gave sysadmin privilege
to the SPN domain account on the database o/w  it is not delegating. Looking for any less privileged a/c to impersonate the user from RS.

Any thoughts...

hi,

Kerberos authentication is supported in both Reporting Services deployment modes: Native and SharePoint integrated. With native mode, you can use a Web-based tool such as Report Manager, to upload and manage reports, models, and other items. With SharePoint integrated mode, you can integrate a Reporting Services service environment with a SharePoint product or technology to upload and manage reports, models, and other items.

Hello, thank you for explanation. however I was not looking for the theory...  Just to clarify that domain account that is impersonating logon user from reporting server to the database server Does need to have sysadmin account ? Is it mandatory? Thanks 

hi refer here:-

http://www.windowsitpro.com/article/migration/mixed-mode-vs-native-mode

http://www.sql-server-performance.com/2009/security-audit-server-level/