The app is single tenant authentication so users must be present in contoso directory.
https://docs.microsoft.com/en-us/azure/active-directory/develop/single-and-multi-tenant-apps With Azure AD B2B, external users authenticate to their home directory, but have a representation in your directory.
https://docs.microsoft.com/en-us/azure/active-directory/governance/entitlement-management-external-users

Explanation:
https://docs.microsoft.com/en-us/azure/traffic-manager/traffic-manager-routing-methods#priority-traffic-routing-method

Explanation:
1. For the blobs - a user delegation SAS only
To maximize security it's better to use a user delegation SAS:
From docs: As a security best practice, we recommend that you use Azure AD credentials when possible, rather than the account key, which can be more easily compromised. When your application design requires shared access signatures, use Azure AD credentials to create a user delegation SAS to help ensure better security.
This also prevents using shared keys & supports time-limited access. Note: user delegation SAS do not support stored access policies.
2. For the file shares - Azure AD credentials
It fulfills the requirement to maximize security (the most secure way recommended by Microsoft), but doesn't support time-limited access, which is optional and has lower priority than security.
https://learn.microsoft.com/en-us/rest/api/storageservices/create-user-delegation-sas.

[C]
Azure Monitor Application Insights supports synthetic transaction monitoring to simulate user interactions and identify UI failures by using availability tests and Playwright-based tests to verify functionality and performance from different locations globally. You can configure these tests to perform various actions, such as opening URLs and performing complex user workflows, which then generate telemetry to report availability, performance, and failures.
[A]
Log Analytics Workspace Insights is a feature within Azure Monitor that provides a unified, graphical view of your Log Analytics workspace's usage, performance, health, connected agents, query activity, and change log. It offers a centralized dashboard to help you monitor and understand your workspaces, enabling operational teams to track health, identify trends, and ensure continuous improvement of your log collection and monitoring strategy.
Reference:
https://learn.microsoft.com/en-us/azure/azure-monitor/app/app-insights-overview
https://learn.microsoft.com/en-us/azure/azure-monitor/logs/log-analytics-workspace-insights- overview