MMMB - a forum script with PGP authorization/authentication

I made a bit of a cypherpunk experiment - PHP textboard forum script that
 uses PGP for authorization of posting messages (messages must be PGP
 signed to pass). It also requires Argon2 PoW to register a key with the
 forum as a kind of an anti-spam measure.
https://codeberg.org/grgmusk/mmmb
To post messages a user has to
1. Register theirs PGP key (there's a link in page top) by submitting
 public PGP key and Argon2 hash of it's fingerprint calculated with
 forum's required parameters (they're on the registration page,
 configurable in forum settings)
( echo -n ABCD1FGHIJA2CDEFG3IJABC4EFGH6JABC8EFGHIJ|argon2 sOmEsAlT123 -t
 60 -k 471040 -p 1)
2. Sign a message with that PGP key, put it into form in New thread/Reply
 link.

I'm not even sure if it all works as intended lol.
I'll try running a live demo at
Tor: http://e5avrgc4ra2xxrrlfnobspec4vcntpro25gwtybxljufo6eukmlri6yd.onion/mmmb_en/
I2P: http://smr6fuqbpfhqtx2ffw6qrtkf6ddhe2v25inrz25kh2sfiejwmosa.b32.i2p/mmmb_en/
shortly after sending this news article. It won't run long, maybe for a
 day. Please try posting something.