Preventing automated sign-ups

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Style Pass

2024-10-02 16:30:03

The Session goes through periods of getting spammed with automated sign-ups. I’m not sure why. It’s not like they do anything with the accounts. They’re just created and then they sit there (until I delete them).

In the past I’ve dealt with them in an ad-hoc way. If the sign-ups were all coming from the same IP addresses, I could block them. If the sign-ups showed some pattern in the usernames or emails, I could use that to block them.

I knew what I didn’t want to do. I didn’t want to put any obstacles in the way of genuine sign-ups. There’d be no CAPTCHAs or other “prove you’re a human” shite. That’s the airport security model: inconvenience everyone to stop a tiny number of bad actors.

The first step I took was the bare minimum. I added two form fields—called “wheat” and “chaff”—that are randomly generated every time the sign-up form is loaded. There’s a connection between those two fields that I can check on the server.

See how the fields are generated from a combination of random bytes and a string of characters never revealed on the client? To keep it from goint stale, this string—the salt—includes something related to the current date.