I have users registering on my website and I need them to verify their website (domain name). Every user has a unique ID, I need my website to generate a file which contains that unique ID and for them to store it on their website, and for my website to then check if the file is there and if the contents of that file are correct (contains the user ID).
It needs to be secure so that the user feels comfortable uploading it to their site AND secure so that when my website downloads and reads it it won't be possible to hack/inject code on my site!
After verifying that everything is correct it will run a dummy PHP function which will confirm it has been successful.
All I need is the code/files, doesn't have to look pretty, and some instructions on how to use. Please test it yourself before submitting to me to ensure it works!