It seems a little pointless, surely every server actually accepting SSH passwords has been 0wned year ago.
My solution is convoluted: On my NAS I have a PHP form that accepts a password, when it's correct, set a flag (in the form of touching a file), and every minute a cronjob runs a bash script to check for the existence of the file: if it exists, then run a python script to talk UPnP to my home router to tell it to forward port ___22 to my NAS' port 22.
Hmm, probably running a VPN server, like WireGuard, makes more sense..
Another possible way would be port knocking. (I had previously set up port knocking on my HTTP server, but there seems to be a bug in the kernel (or in some driver) that prevents it from working correctly, so now the HTTP is not available. Using port knocking to restrict access to HTTP is probably not common, and might prevent your solution from being used if the form uses HTTP.)
Running over a VPN service would have the much the same effect.