Programming :: Make Data Persist Through Webpages Via Forms?

For a website I'm making in PHP, I need a link on a particular dynamically generated page, called "Make a friend". Clicking this will take the user to a page where they have to provide their username and password, and if it's correct, the database will be updated. When the "make a friend" page is generated, the link will have a ?author=32 (say) argument, to reflect the author's id in the database. Now my problem is, that I need the author AND username and password as arguments to the "make a friend" script. How do I do this?
Instead of making the link a link, I've been toying with the idea of making it a form button (which will look better anyway), and using a <input type="hidden"> argument, for the NEXT page, which will be the page requesting the username and password, but I still can't seem to come up with a viable solution somehows.