curl -i -X POST "https://api.box.com/2.0/comments" \
     -H "authorization: Bearer <ACCESS_TOKEN>" \
     -H "content-type: application/json" \
     -d '{
       "message": "Review completed!",
       "item": {
         "type": "file",
         "id": 426436
       }
     }'

{
  "id": "11446498",
  "type": "comment",
  "is_reply_comment": true,
  "message": "@Aaron Levie these tigers are cool!",
  "created_by": {
    "id": "11446498",
    "type": "user",
    "name": "Aaron Levie",
    "login": "ceo@example.com"
  },
  "created_at": "2012-12-12T10:53:43-08:00",
  "modified_at": "2012-12-12T10:53:43-08:00",
  "item": {
    "id": "11446498",
    "type": "file"
  },
  "tagged_message": "@[1234567:Aaron Levie] these tigers are cool!"
}