How to Build a One-Time QR Code with URL Redirect

Requirement

https://t.me/blacktechsharing/183161

Approach

A QR code is essentially a string of characters embedded in an image. This string can be a URL.

Since the QR code image has already been sent to others, and you can't go to their computer or phone to delete the image, how is a "one-time QR code" implemented?

If the QR code image stays the same, then the URL A corresponding to the QR code stays the same.

When you visit URL A, you're accessing a server. This server can make everyone who visits URL A redirect to a new URL B.

We define URL B as the URL that actually carries the real meaning. We let the server allow only the first visitor to URL A to be redirected to URL B; subsequent visits to URL A will have the redirection disabled.

This is how a "one-time QR code" is implemented.

For example,

The URL with actual meaning is https://google.com

We set up a server, https://1way.eu.org

We make https://1way.eu.org/HcAx62 redirect to https://google.com and only redirect once.

We generate a QR code using https://1way.eu.org/HcAx62.

When someone scans this QR code, they will visit https://1way.eu.org/HcAx62, the system redirects them to https://google.com, and then the system records that this https://1way.eu.org/HcAx62 is now invalid.

If someone else scans this QR code, they will also visit https://1way.eu.org/HcAx62, but the system will tell them that this resource is no longer valid.