In newer versions of IIS it is possible to use a new built-in user definition as the identity for application pools, namely the "ApplicationPooIdentity". the IIS extension should support this as input to the <iis:WebAppPool Identity="..."/> element.
trackback from "IIS extension+=ApPI" pull request https://wix.codeplex.com/SourceControl/network/forks/ursoft/ApplicationPooIdentity/contribution/3431
trackback from "IIS extension+=ApPI" pull request
https://wix.codeplex.com/SourceControl/network/forks/ursoft/ApplicationPooIdentity/contribution/3431