curl -i -X PUT "https://api.box.com/2.0/task_assignments/12345" \
     -H "authorization: Bearer <ACCESS_TOKEN>" \
     -H "content-type: application/json" \
     -d '{
       "message": "New message",
       "resolution_state": "completed"
     }'

{
  "id": "11446498",
  "type": "task_assignment",
  "item": {
    "id": "12345",
    "type": "file",
    "etag": "1",
    "sequence_id": "3",
    "name": "Contract.pdf",
    "sha1": "85136C79CBF9FE36BB9D05D0639C70C265C18D37",
    "file_version": {
      "id": "12345",
      "type": "file_version",
      "sha1": "134b65991ed521fcfe4724b7d814ab8ded5185dc"
    }
  },
  "assigned_to": {
    "id": "11446498",
    "type": "user",
    "name": "Aaron Levie",
    "login": "ceo@example.com"
  },
  "message": "Please review",
  "completed_at": "2012-12-12T10:53:43-08:00",
  "assigned_at": "2012-12-12T10:53:43-08:00",
  "reminded_at": "2012-12-12T10:53:43-08:00",
  "resolution_state": "incomplete",
  "assigned_by": {
    "id": "11446498",
    "type": "user",
    "name": "Aaron Levie",
    "login": "ceo@example.com"
  }
}