Application Express :: Creating Functionality For Changing Users Password

I'm trying to create a functionality on my application that lets the user change their password whenever they want or when the password gets expired.

But to do that, first I need a Branch to the page "Password Change" whenever the login procedure returns "Password Expire", but when the user has an expired password he can't access none of the pages of the application.

My other problem is:

Even if I can get the user to be redirect to the "Password Change" page, I would need a function that validate his current expired password, because in order to alter his own, he would need to inform his current password and the new one he desires. If I was using Apex Authentication that would be very easy I think, but I'm obligate to use Database Account Authentication.