Here is a script that purge the 'TokenAndPermUserStore' every time it reaches 100MB.
DECLARE @CacheSize int
DECLARE @CurDate varchar(30)
WHILE (1=1)
BEGIN
SET @CurDate = CONVERT (varchar, GETDATE(), 126)
SELECT @CacheSize = SUM(single_pages_kb + multi_pages_kb)
FROM sys.dm_os_memory_clerks
WHERE name = 'TokenAndPermUserStore'
-- Greater than 100MB
IF @CacheSize >= 100000
DBCC FREESYSTEMCACHE ('TokenAndPermUserStore')
RAISERROR ('Cleared TokenAndPermUserStore at %s, size = %dKB', 0, 1, @CurDate,
@CacheSize) WITH LOG
END
RAISERROR ('TokenAndPermUserStore size at %s: %dKB', 0, 1, @CurDate, @CacheSize)
WITH NOWAIT
WAITFOR DELAY '00:00:10'