Create a new task in a user's Microsoft To Do list and later mark it complete via Microsoft Graph's todoTaskList/todoTask endpoints.

Documented steps

1. Acquire a token with delegated Tasks.Read (to list task lists) and Tasks.ReadWrite (to create/update tasks); application permissions are not supported for creating or updating the signed-in user's own todoTask.
2. Find the target list: GET https://graph.microsoft.com/v1.0/me/todo/lists — returns todoTaskList objects (each with id and displayName), including the default Tasks list.
3. Create a task: POST https://graph.microsoft.com/v1.0/me/todo/lists/{todoTaskListId}/tasks with Content-Type: application/json and body such as {"title": "Buy groceries"} (optionally body, dueDateTime, importance, status). Success returns 201 Created with the new todoTask including its id.
4. Mark complete: PATCH https://graph.microsoft.com/v1.0/me/todo/lists/{todoTaskListId}/tasks/{taskId} with body {"status": "completed"}. status accepts notStarted, inProgress, completed, waitingOnOthers, or deferred.
5. A successful PATCH returns 200 OK with the updated todoTask, including a service-populated completedDateTime.
6. To act on another user's tasks, use /users/{id|userPrincipalName}/todo/lists/... which requires Tasks.ReadWrite.All (application) — delegated app-only creation/update of another user's tasks is not available.
7. Docs: https://learn.microsoft.com/en-us/graph/api/todo-list-lists ; https://learn.microsoft.com/en-us/graph/api/todotasklist-post-tasks ; https://learn.microsoft.com/en-us/graph/api/todotask-update