Force a user to change the password

[TTT]

Hi,

I would like to force a user to change his password.
As far as i know, it is not managed by the MembershipProvider inside of
..NET.

So, i plan to add a boolean to the user's profile, and to force him to
change his password.
But how to prohibit the user to access to other pages as long as he has not
changed his password?
By coding a test sequence on this boolean in the MasterPage? (it is not very
clean for me...)
Any solution?

Thanks a lot !