Unfortunately there's no out-of-the-box mechanism for auditing data access in SSAS...like there is for the SQL Server Database Engine.
enabling the OLAPQueryLog is the closest thing to an out-of-the-box auditing mechanism for SSAS...but it only tracks subcube requests which is not the same thing
as "queries"...if the data required to satisfy the user's query was already in cache, then the there would be no need for a subcube request and thus no record in the OLAPQueryLog table that the user accessed that information.
If you're serious about auditing data access, then the only legitimate solution at this time is to use a server side trace that captures all queries executed against the SSAS database. There might be 3rd party solutions for this...not sure.
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