使用HTTP Web请求发送HTTP标头以进行NTLM身份验证

I want to login to a Sharepoint portal which brings up a login dialog but is using NTLM authentication. How can I modify the HTTP headers in C# to make a successful login request? I assume I would need to make a HTTPWebRequest to a page within the logged in section of the portal and post the HTTP headers collection alongside this?I want to login to a Sharepoint portal which br