title: SharePoint REST - Change Author on file
body: <p>Having a difficult time changing the author of a sharepoint item such as a file.
  The actual jsonstring i am using:</p>
  
  <pre><code>{'__metadata': { 'type': 'SP.Data.DocumentsItem' } ,'AuthorId': '20'}
  </code></pre>
  
  <p>Posted to this url:</p>
  
  <pre><code>https://mysharepoint.sharepoint.com/sites/mysite/_api/web/lists/getByTitle('Documents')/items(137)
  </code></pre>
  
  <p>I have set Created By to Readonly=false which works fine, but the Created By or Modified By is not changing and i am not getting errors. 
  Do i need something else in my request?</p>
  
  <p>Thanks!</p>