Needing a login is dependent on the other site. With CFHTTP,
you are retrieving whatever content is returned to the browser. The
other web site "sees" this visit as just another visitor on the
web. If the page you are visiting is unprotected, you wont need a
login.
Once you use CFHTTP, the contents of the page in question are
returned to you as a variable. Use your string functions to parse
or search that variable for whatever word or words you like. If
your search finds your string, you can be reasonably sure that your
link appears on the other site. I say "reasonably sure" because the
other site may be capable of "fooling the system" and not actually
displaying the link correctly, or hiding it in the same font color
as the background color, etc. etc.