Introduce video and explain keyless authentication benefits

Added a video introduction and expanded on the benefits of Microsoft Entra ID Managed Identities for secure authentication.

Author: staleycyn

learn-pr/wwl-azure/manage-secure-ai-ready-infrastructure/includes/3-implement-keyless-authentication-microsoft.md

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+The video introduces the key concepts covered on this page. 
+
+> [!VIDEO https://learn-video.azurefd.net/vod/player?id=553f19b1-ef39-4351-a334-107927c6decf]
+
 You've just configured RBAC roles to grant your AI agent precise permissions for reading conversation history from Cosmos DB. However, the agent still needs a way to prove its identity when making API calls—traditionally accomplished by storing a connection string or access key in application configuration. This approach creates immediate security risks: developers accidentally commit secrets to source control repositories, connection strings proliferate across configuration files in multiple environments, and operations teams spend hours rotating credentials quarterly to satisfy compliance audits. Microsoft security research shows that 60% of cloud security incidents involve compromised credentials, with an average breach detection time of 280 days.
 
 Microsoft Entra ID Managed Identities eliminate credential storage entirely by providing your Azure resources with automatically managed identities that can authenticate to any service supporting Entra ID authentication. Unlike traditional service principals that require manual creation and credential management, managed identities have their lifecycle tied directly to the Azure resource that uses them. When you enable a system-assigned managed identity on an App Service, Azure automatically provisions an identity in your Entra ID tenant, manages its credentials behind the scenes, and rotates the underlying certificate every 46 days without any action from your operations team.