Complete a task — transition any task to COMPLETED by applying its unique completion action. For approval tasks this is the "approve" primitive.

Common uses:

• Approve an access request (task with task_category=APPROVAL and product_area=APPSTORE).
• Mark a non-approval task done when it exposes exactly one action that transitions to COMPLETED (e.g. acknowledging a manual provisioning step). Tasks with multiple possible completion actions should use POST /tasks/{task_id}/perform-action instead.

This endpoint resolves the unique action on the task that transitions it to COMPLETED and applies it on behalf of the caller. The caller must be an assignee of the task (or a domain admin). There is no request body.

Responses:

• 204 No Content — task completed.
• 403 Forbidden — caller is not authorized to act on the task.
• 409 Conflict — task is already in the requested status (safe to treat as idempotent).
• 404 Not Found — task does not exist in this domain, or the Tasks API is not enabled.

To deny instead of approve, use POST /tasks/{task_id}/dismiss. For tasks that expose custom workflow actions (not approvals), use POST /tasks/{task_id}/perform-action.