Login data flow question

Does login username and password goes directly to authorisation URL that is set or do they go to wordpress site widget is on first and then get redirected to authorisation. I have a feeling that they go directly, but need confirmation. I could set up WordPress on localhost and test it with fiddler, but it takes time and it would be easyer if someone would just tell me.
Thank you.

http://ww.wp.xz.cn/extend/plugins/sidebar-login/