Support application permissions (app‑only / Managed Identity) for Planner Task Chat Messages API

Request
Please add Application (app‑only) permission support for Planner task chat messages:

• GET https://graph.microsoft.com/beta/planner/tasks/{task-id}/messages

Current limitation
This endpoint is currently delegated-only (works when signed in as a user) and does not work for Managed Identity / app‑only automation scenarios (e.g., Azure Automation Runbooks). This blocks unattended exports and reporting.

Why this matters (business impact)

• We run scheduled Azure Automation Runbooks (Managed Identity) to export Planner data for governance and Power BI reporting.
• The “new Planner” experience uses task chat messages as the primary comment mechanism, and these messages are required for audit/reporting.
• Without app‑only access, organisations are forced into less secure patterns (service accounts, interactive token flows) that complicate compliance.

What we want (minimum viable)

1. Read-only app permission support to list messages (equivalent of “read task chat”).
2. Least-privileged permission option such as Tasks.Read.All for app-only (or a new narrower scope if preferred).
3. Standard access enforcement (only return messages for tasks/plans the app is allowed to read).

Why app-only is needed
Managed Identity is the recommended secure pattern for Azure-native automation. Requiring delegated auth prevents reliable unattended reporting at enterprise scale.

Many thanks