How to update created and modified properties of a file in sharepoint online using REST in C#

Hi,

How to update the modified date and the created date to my own value of an item in document library using REST API in c#.

var body = "{ '__metadata': {'type':'SP.ListItem'},'Modified':'2012-03-30T17:24:17Z'}";

var json = client.UploadString(url, body);

Thanks.