Not sure what you mean by login by window form app.
Window application can access a websites via HttpClient calling a webapi, or if html pages, using screen scraping technology. The other option is to host a webview control.
Passing authentication to the website depends on how authentication is handled on the website. It may use bearer tokens, basic authentication, Kerberos or windows authentication. The other option is a login page that uses cookies. There may even be a central login server.