In the previous post I described the problem of accessing WebDav resources by using WebDav on a sharepoint server which has enabled form based authentication. The basic idea behind the solution is actually quite easy:

When accessing the sharepoint portal on the external zone with the ASP.NET membership accounts you have to fill out the login form with your credentials. When you click on the “Sign In” button a HTTP Post is sent to the server containing some uniquely generated IDs for your current browser session and your credentials with the name of the containing form component in plain text. If the authentication is successful the server returns a cookie containing the authorization state of the client. This cookie must be saved in the clients session and provided to the server every time the client communicates with it.

.NET, Security Formbased Authentication, Sharepoint, WebDav