[AppService]Update auth configuration instructions for ACR pulls

[sarsharma]

Add note about Azure Container Registry configuration for managed identity to ensure authentication-as-arm is enabled for ACR image pulls
Note is similar to the auth policy requirement for Azure Container Apps : https://learn.microsoft.com/en-us/azure/container-apps/managed-identity-image-pull

[prmerger-automator]

@sarsharma : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit ac3bd1e:

✅ Validation status: passed

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articles/app-service/configure-custom-container.md	✅Succeeded

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[v-regandowner]

@msangapu-msft

Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds guidance for App Service custom container deployments that use managed identity to pull images from Azure Container Registry (ACR), specifically calling out the requirement for ARM-audience token support (“authentication-as-arm”) in ACR.

Changes:

• Added an IMPORTANT note explaining the ACR “authentication-as-arm” requirement for managed-identity pulls.
• Included Azure CLI commands to check/enable the setting and a documentation link for more details.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

[learn-build-service-prod]

Learn Build status updates of commit 58965c9:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/app-service/configure-custom-container.md	✅Succeeded

For more details, please refer to the build report.

[learn-build-service-prod]

Learn Build status updates of commit cb8f4f0:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/app-service/configure-custom-container.md	✅Succeeded

For more details, please refer to the build report.