Hi i wish to give a "register" link in to the apache authentication popup. enter image description here

i'd like to alter the mistake message page that's known as whenever you press cancel. i investigated directory www/error where i discovered some files however it appear none of individuals files may be the error page that's known as. how do i discover the Authorization Needed page that's known as ? in order to change it out.

You cannot - that's native browser behavior, no Apache popup. Try different browsers and find out the way they perform the popup in a different way.