How to reuse Active Directory / LDAP Credentials in Webservice connection?

Hi, we handle Aras logins via Active directory. A second software shall be connected via Webservice/HttpWebRequest. This software share the same Active Directory Accounts. Regular connection strings in Aras may look somehow like this:

string username= "myuser";
string password="mypw";
string encoded = System.Convert.ToBase64String(System.Text.Encoding.GetEncoding("ISO-8859-1").GetBytes(username+":"+password));
HttpWebRequest request = (HttpWebRequest) WebRequest.Create("http://xyz");
request.Headers.Add("Authorization","Basic "+encoded);

On local machines, it´s possible to use this line of code for using Windows access data: request.Credentials = CredentialCache.DefaultNetworkCredentials; But as Aras is running on a server, this Method will not return the credentials of the current user. Are there samples available, that show how to forward the user credentials? I have seen, that the Aras Sharepoint integration does something similar, especially the Method SPDocument_onGet. But I am not sure, if this code is reusable, as it links to some Sharepoint specific files in the codetree. Maybe there are some other samples available, which are easier to use? Thanks for your help! Angela