Controlling Access for Trial Subscription

[keithxjr]

I've been tasked to build a system that allows someone in our company to send out an email with a link to a pdf file that will be kept on our webserver. The recipient can follow the link to view a newsletter we normally sell. The idea is we do this for three months, then see if they'd like to continue and pay for the full subscription.I've got the registration portion built, but I'm trying to find the best solution for sending the email. Here's what I've thought of, but am interested if anyone else has something better..1) When emailing, generate a generic code that gets appended to the URL. The use would follow the url, and it would check our DB for "ok" entries and pass/fail them access. This seems ok, but a link could be passed around or even loaded to a public site where anyone could access.2) To extend the above, I thought maybe I'd have a "one time click" kind of thing where once I know the link was clicked, it could expire, so any subsequent clicks fail. The downside is if they click to view and close their window, they're done. Likewise, if they click and their computer crashes before download completes, they'd be locked out as well. I don't know if there's a way (in PHP for me) to confirm a file download has completed...3) I could put the files in a directory like /trials/201009/[email protected] where the file is uploaded and the name for the link is random so it would be hard to guess. Then I could use .htaccess to protect each month's folder with a different password. This could get tedious and would be annoying for users most likely.We don't want to force them to manage their own passwords b/c having to login and remember yet another account may discourage participation.Thanks for any ideas or pointers.D.