Bookstack - Sign Up
Click on the "Sign Up" button on the top-right corner of the screen:
Click "sign up with microsoft azure"
You'll be redirected to O365 where you can log in using your email credentials. If you have MFA enabled, (highly recommended- ask help desk for more information) you'll be prompted to enter your code.
The first time you log in, you'll be asked if you'd like to allow the app "bookstack" to be trusted. You do.
You'll then get an email confirmation to verify your account. Once that's done you can log in using Microsoft Azure.