MSXML2.ServerXMLHTTP Question

I've used MSXML2.ServerXMLHTTP in ASP to write a link checker. It checks a list of URLs stored in a db and flags any websites/webpages that are down. Since I am only interested in whether the page is up or not and not in the actual HTML, I use HEAD instead or GET.

Code:

Set getPage = Server.CreateObject("MSXML2.ServerXMLHTTP")
getPage.Open "HEAD", URL, false
where getPage is my object, URL is the URL to check
and I can also do

Code:
Set getPage = Server.CreateObject("MSXML2.ServerXMLHTTP")
getPage.Open "HEAD", URL, false , username , password

which checks the URL using the username and password supplied. Everything works as expected but my problem lies in the fact that the password is in plaintext in the ASP page. It is not good security practice to have an ASP page contain a username/password combo in plaintext. This means that if someone had file access to the ASP page (intranet) then they could see the username/password pair which we want to try
and avoid.

Does the HTTP standard only allow for username/passwords to be sent in plaintext?