Explanation:

Box 1: An Azure AD app registration
Azure active directory (AD) provides cloud based directory and identity management services.You can use azure AD to manage users of your application and authenticate access to your applications using azure active directory.
You register your application with Azure active directory tenant.
Box 2: A conditional access policy
Conditional Access policies at their simplest are if-then statements, if a user wants to access a resource, then they must complete an action.
By using Conditional Access policies, you can apply the right access controls when needed to keep your organization secure and stay out of your user ' s way when not needed.

Reference:
https://codingcanvas.com/using-azure-active-directory-authentication-in-your-web-application/
https://docs.microsoft.com/en-us/azure/active-directory/conditional-access/overview
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/walkthrough-register-app-azure-active- directory#:~:text=Create%20an%20application%20registration%201%20Create%20an%20application,the%
20options%20and%20click%20on%20Add%20permissions.%20
" After consenting to use their Dataverse account with the ISV ' s application, end users can connect to Dataverse environment from external application. The consent form is not displayed again to other users after the first user who has already consented to use the ISV ' s app. Apps registered in Azure Active Directory are multi-tenant, which implies that other Dataverse users from other tenant can connect to their environment using the ISV ' s app. "

Reference:
https://docs.microsoft.com/en-us/azure/storage/queues/storage-tutorial-queues

A: Application Proxy is a feature of Azure AD that enables users to access on-premises web applications from a remote client. Application Proxy includes both the Application Proxy service which runs in the cloud, and the Application Proxy connector which runs on an on-premises server.
You can configure single sign-on to an Application Proxy application.
C: Microsoft recommends using Application Proxy with pre-authentication and Conditional Access policies for remote access from the internet. An approach to provide Conditional Access for intranet use is to modernize applications so they can directly authenticate with AAD.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/app-proxy/application-proxy-config-sso-how-to
https://docs.microsoft.com/en-us/azure/active-directory/app-proxy/application-proxy-deployment-plan

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