(looking for) specific type of web chat

many times I find myself in situations where I’m on some computer which is totally isolated - friends computer, completely newly installed (VM), some corporate remote desktop where I can’t install anything — and I need to transfer some information to this computer.

Ideally what I would have is:

• some sort of web chat
• self hosted (so that I can spin it up only when I need it, and that I can “destroy” all the data after each session)
• simple URL where you specify a room name edit it (eg.: domain.com/qck-321)
• on open you specify username (no other authentication)
• first person who joins needs to confirm all the others (so people can’t just “drop in”)
• no fancy technology (web sockets,…)

what I found so far:

• https://tlk.io/ - quite close but not all points
• https://chitchatter.im/ - this one is quite promising but unfortunately it failed me on first windows remote machine (probably due to some firewall rule)

I’m more that prepared to develop something my self but first I would like to check if there is really nothing out there to solve this.

Bonus question- do you have any other approach - how do you transfer (potentially sensitive) information to a “isolated” machine?