It is connected to the flic app on a user's mobile phone. The internet call on a long press goes via the flic app's internet call to the webserver's script. They use a browser on their phone to run the local script that is paused waiting for the webserver's script to respond in some way to validate they have used an authorised Flic button with a valid serial number. At least that is what I am trying to achieve.

I was not intending running an app on the clients device, just a PHP script that says "long press your flic button now to gain access to your account" the long press does an internet call to a script on the server. I was hoping that the server script could use the Flic serial number to grant permission to the client script via a database entry or some form of cookie or client/server comms such as ajax/xml once the serial number was validated by the remote script.

I was hoping to use flic buttons as a security device. when the flic button does a long click it can be set to run a script on my website. This script can pick up various pieces of information such as the flic serial, the IP of the client, the client's machine make and model etc. I can look up the Flic serial number in a database and get the assigned user's name etc. to display on the clients screen.
However, there does not seem to be a way to guarantee that the flic button came from a specific client. perhaps two buttons arrive at once.
The IP might be a shared IP of a common router, the devices could be the same make and model so I cant use that.
I cannot create local cookies or PHP session variables since those are specific to the user's browser and the triggered script does not use their browser.
Does anyone use Flic buttons as a security device?
Any suggestions would be welcome.

@Emil
Thanks for the reply. I will try this. The obvious follow-on question is "will there be an IOS equivalent option?"

Is there a way to save my flic button settings? I have a single flic 2 (no hub) and want to use it for home automation when at home then for a specific app when at work. It would be useful if the settings could be saved in the app and re-loaded easily and quickly rather than manually reprogam the settings in the app each time.

I wanted a flic holder (£5) but the delivery charge to UK would be £16. there is no alternative shipping method offered.
A slower cheaper delivery method should be available.