I have not used the method you have illustrated but it looks to me that this will only test what the previous page was.
It will not test that the user has been authenticated, logged on or any other code on default.asp has been executed.
If you wish the user to be logged on to your site I suggest using a session variable to when they successfully log on such as a logonID.
Then test that on your further asp pages.
They say, best men are moulded out of faults,
And, for the most, become much more the better
For being a little bad.