Azure Policy evaluates resources in Azure by comparing the properties of those resources to business rules.
Once your business rules have been formed, the policy definition or initiative is assigned to any scope of resources that Azure supports, such as management groups, subscriptions, resource groups, or individual resources.
Reference:
https://docs.microsoft.com/en-us/azure/governance/policy/overview

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

Topic 3, Contoso
Existing Environment
Technical Environment
The on-premises network contains a single Active Directory domain named contoso.com.
Contoso has a single Azure subscription.
Existing Environment: Business Partnerships
Contoso has a business partnership with Fabrikam, Inc. Fabrikam users access some Contoso applications over the internet by using Azure Active Directory (Azure AD) guest accounts.
Requirements: Planned Changes
Contoso plans to deploy two applications named App1 and App2 to Azure.
Requirements: App1
App1 will be a Python web app hosted in Azure App Service that requires a Linux runtime. Users from Contoso and Fabrikam will access App1.
App1 will access several services that require third-party credentials and access strings. The credentials and access strings are stored in Azure Key Vault.
App1 will have six instances: three in the East US Azure region and three in the West Europe Azure region.
App1 has the following data requirements:
Each instance will write data to a data store in the same availability zone as the instance.
Data written by any App1 instance must be visible to all App1 instances.
App1 will only be accessible from the internet. App1 has the following connection requirements:
Connections to App1 must pass through a web application firewall (WAF).
Connections to App1 must be active-active load balanced between instances.
All connections to App1 from North America must be directed to the East US region. All other connections must be directed to the West Europe region.
Every hour, you will run a maintenance task by invoking a PowerShell script that copies files from all the App1 instances. The PowerShell script will run from a central location.
Requirements: App2
App2 will be a NET app hosted in App Service that requires a Windows runtime. App2 has the following file storage requirements:
Save files to an Azure Storage account.
Replicate files to an on-premises location.
Ensure that on-premises clients can read the files over the LAN by using the SMB protocol.
You need to monitor App2 to analyze how long it takes to perform different transactions within the application. The solution must not require changes to the application code.
Application Development Requirements
Application developers will constantly develop new versions of App1 and App2. The development process must meet the following requirements:
A staging instance of a new application version must be deployed to the application host before the new version is used in production.
After testing the new version, the staging version of the application will replace the production version.
The switch to the new application version from staging to production must occur without any downtime of the application.
Identity Requirements
Contoso identifies the following requirements for managing Fabrikam access to resources:
Every month, an account manager at Fabrikam must review which Fabrikam users have access permissions to App1. Accounts that no longer need permissions must be removed as guests.
The solution must minimize development effort.
Security Requirement
All secrets used by Azure services must be stored in Azure Key Vault.
Services that require credentials must have the credentials tied to the service instance. The credentials must NOT be shared between services.

Reference:
https://docs.microsoft.com/en-us/azure/virtual-machines/dedicated-hosts
https://docs.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-autoscale-overview

Azure Resource Policy Definitions can be used which can be applied to a specific Resource Group with the App Service instances.
Reference:
https://docs.microsoft.com/en-us/azure/governance/policy/overview