Since documentation on this process is very vague and confusing (or old), I wanted to verify that I was doing it correctly and not missing any steps.
I am trying to
There's a problem in your authorization tag, should be:
because you want to deny anonymous users. If you fix this, you can safely remove all the stuff from the master page and global.asax - you don't have to remap the forms identity to your own custom identity stored in session. It's the waste of resources and I don't think it raises the security of your solution in a significant way. You can rely on the forms cookie.