Whether you need a license or subscription depends on which features you plan to use in Azure. I would check out the pricing pages for the features you are using.
For app services, see: https://azure.microsoft.com/en-us/pricing/details/app-service/windows/
For Azure Active Directory there are object limitations for some of the lower licenses. For example, the free version has a 500,000 object limit. I would also visit the pricing page for Azure Active Directory: https://azure.microsoft.com/en-us/pricing/details/active-directory/#:~:text=Azure%20Active%20Directory%20comes%20in,%2C%20Intune%2C%20and%20Power%20Platform.
I can try to answer if you have specific questions about the licenses required for features in your app, but I would suggest reaching out to your licensing representative of choice for these types of questions since licensing isn't a supported topic on Q&A. https://azure.microsoft.com/en-us/support/create-ticket/