Active Directory MultiTenant and Asp.net MVC

I'm reading about AD in azure and its integration with Asp.net MVC

But I have with some doubts.

When using AD must not use more another provider? For example ASP.NET Identity?

Since the AD has a multi tenant deployment, as I seto the tenant to the user?

The AD user is only registered by azure panel? I can not register via application?

I would like to create a multi tenant application

And the user to create an account trial

As this site: https://www.xero.com/signup/
Can I use AD for that? I will not use authentication with social networks

Can anyone give me a direction