ASP.NET Windows Authentication logout

Question

How do you logout when using Windows authentication in ASP.NET like this web.config?

<authentication mode="Windows" />

I've already tried the following unsuccessfully. It redirects, but does not log out the user.

void logoutButton_Click(object sender, EventArgs e) {
    HttpContext.Current.Session.Clear();
    HttpContext.Current.Session.Abandon();
    ViewState.Clear();
    FormsAuthentication.SignOut();
    Response.Redirect("/");
}

Background Info:

I have to use Windows authentication because I need to impersonate the identity using Active Directory to gain access to local files. And I cannot impersonate using Forms authentication because the HttpContext.Current.User.Identity won't be a WindowsIdentity. Impersonate using Forms Authentication

Answer 1

No server-side logout button will work when using "Windows" authentication. You must use "Forms" authentication if you want a logout button, or close the user's browser.

Answer 2

For IE browsers only, you can use the following javascript to logout the user if using Windows Authentication. (Note: closing the browser isn't required, but recommended since the user might be using a non-IE browser).

If the user clicks "No" to close the browser, then the user will be prompted for a username/password if they attempt to access a page on the site that requires authentication.

try {
   document.execCommand("ClearAuthenticationCache");
}
catch (e) { }
window.close();

This code was taken from SharePoint's Signout.aspx page.

Answer 3

Windows authentication works at the IIS level by passing your Windows authentication token. Since authentication occurs at the IIS level you cannot actually log out from application code. However, there seems to be an answer to your problem here. It is the second question addressed and essentially involves using Forms Authentication and the LogonUser Windows api.