如何在C＃中读取安全的XML URI？

I am trying to read a secure XML document from a URI in C#. I understand the basics of the XmlReader class. However I cannot figure out how to supply a username and password for the URI in code. I get the feeling it has something to do with an XmlSecureResolver object. But I can't figure out how to set the username and password. Can anyone help me with how to set the credentials?I am trying to read a secure XML document from