Caching in getAuthAssignments

Would anyone have any idea why caching is not implemented in CDbAuthManager::getAuthAssignments()? (file location: /yii/framework/web/auth/CDbAuthManager.php)

I’m using the Rights module in my application, and I’m making many calls to checkAccess(). Fundamentally, this method incorporates a call to getAuthAssignments(), which requires a database call to fetch the user’s assignments. Since I’m performing many access checks for each user’s page request, my application is repeating the same database call in getAuthAssignments() over and over again. This seems like an area that is ripe for caching. I can’t imagine how a user’s authorization assignments would change over the course of a page load. Any thoughts as to why caching hasn’t been implemented here?