Another of our top 3 is Azure Active Directory. Active Directory is an authorization and authentication store. It is where we can create users and assign them passwords. Passwords are one form of authentication, we will get to play with a few more since we are the owners of this Active Directory (AD) instance.
Start in the portal and click on the hamburger in the top left (the stack of short lines) and then on <all resources>
https://login.microsoftonline.com/mynewsecretproject.onmicrosoft.com/oauth2/v2.0/authorizeNotice that the part in italics above is the same thing we had for our Initial domain name. Active Directory controls authorization and authentication for a domain. Before we were all cloudy, enterprises and small businesses would have Domain Controllers which ran AD. Microsoft is hosting our domain within it's own tenant and we are about to log into it! Exciting!