Getting and Setting HTTP - Headers with JSP

Hi,
I am working on a site where when a user get to a page, for security reasons, a UNIX ACL pop-up box comes up.
I need to find a way to set the HTTP - Header with (add username and password to it) when the JSP session is created. If I can set the header with username and password, the pop-up box will not came up. Does anybody know of any JSP methods for getting and setting the HTTP - Header? Any other idea?
Thanks,
Heitor