Website owners to claim their websites by uploading control file ? For my website directory I would like users to be able to claim their own websites.

This is needed to allow only validated and authorized users to edit website-related content. 

I would like the system to ask users automatically to upload a control file with a filename generated in Drupal 7. 

Drupal will check automatically if the filename can be downloaded from the claimed website and if so it will assign authorization to the claimant to edit related content.

How to do this in D7, preferably with existing modules ?
It shouldn't be too difficult to code it:

If you have the website URL and the control file name stored in a node you can use drupal_http_request to perform a GET against the URL and filename.

If you get a status 200 returned the file exists and you can update another field on the node to indicate that the URL has been successfully validated.