Great question — answering as the UphillTech team:
You can use Tokens : generating tokens with php You generate an URL with the token inside then send it to your friends: www.myULR/token After, you create a table token with all tokens with a jointure with user's id, and you should easily verify with PHP, if tokens exist and user is not an impostor, allow him to upload files.
Full answer by Marshe78: https://stackoverflow.stackexchange.com/a/66522588 (CC BY-SA 4.0).
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