Office 365 and Azure Integration - asp.net-mvc

Question

We are planning to integrate Authentication with Office 365 using MVC(.net)and had few questions
I am under the assumption that many organization might have office 365 subscription but it is not mandatory that they should have Azure subscription as well. Is this right?
Under the Office 365 account for an organization, there can be many users(not AD).
If my organization needs to export existing AD users into Office 365, is that the point I should be thinking of Azure subscription or can existing users from AD be directly exported to Office 365

Answer 1

You can use Office 365 (O365) without an Azure Subscription,
however, the directory service used for access to O365 is actually
Azure Active Directory (Azure AD). The default directory namespace
is {subscriptionname}.onmicrosoft.com.
All O365 users will be registered in an Azure AD instance tied to
the O365 subscription.
Existing on-premise users held in Windows Active Directory can be syncronised to Azure AD using the Azure Active Directory Sync Services which is a free tool and which can be used without an Azure Subscription.
If at some later point you wish to use the same Azure AD instance as part of an Azure Subscription it is possible to.

Answer 2

Chris, your first assumption is correct. Customers that have an Office 365 subscription do not necessarily have an Azure subscription too. However this doesn't prohibit them from signing up for applications like yours using their Office 365 Azure AD and using single sign-on with their Office 365 accounts. During sign-up customers will consent to granting your application the required delegated permissions - this experience doesn't require an Azure subscription.
All Office365 accounts live in the Azure Active Directory to which that Office365 subscription is associated. That Azure AD can contain user accounts mastered in the cloud and/or user accounts mastered in an on-premises directory that have been syncronized to the cloud. Many of our customers are small businesses with accounts only in the cloud, whereas our enterprise customers syncronize accounts from on-premises and also create cloud only accounts.
Synchronizing on-premises directory to Office 365 Azure AD also doesn't require an Azure subscription. The Azure AD Sync tool is available outside of an Azure subscription.
Finally, Azure AD administration via the Azure management portal (requires Azure subscription) provides many identity management features that aren't available in the Office365 management portal: Azure AD premium reports including anomalous sign-ins, managing access to third party applications like the one you're building (simple users and groups assignment as well as assigning users and groups to application roles), managing security groups in the cloud and many more.
Read more about Azure AD and most importantly try out both the experiences (without and with Azure subscription).
Hope this helps.