Hi sadarax

I downloaded the API for PHP and look into the source.
It seems that all you need to do is generate an API key and secret key in your DivShare welcome page.
With those in hand you can use LWP (or WWW::Mechanize, but I don't know this module) to post a request to:

http://www.divshare.com/api/?method=login&api_key=API-KEY&user_email=Y
+OUR_EMAIL&user_password=YOUR_PASSORD
[download]

The server will respond with an XML that will have your SESSION_KEY.
Then, from the API documentation, you must request for an UPLOAD_TICKET. Another post:

http://www.divshare.com/api/?method=get_upload_ticket&api_key=API-KEY&
+api_session_key=SESSION_KEY&api_sig=
[download]

Parse the XML for the upload ticket and build the form as shown in http://www.divshare.com/integrate/api#uploading