Register to RoundCube by URL string not working

[kibi]

I'd like to register into RoundCube by sending following URL
http://www.sitename.com/roundcubemail/[email protected]&_pass=123&_action=login

But when I try to send such url – I've got error message.
When I visit my site page http://www.sitename.com/roundcubemail and enter login and password – it's ok.

Could you tell me what should I do to login by url string

Thank you for help