bad
useful for git hosts like https://codeberg.org
on plan9:
; auth/secstore -G factotum | grep rsa | auth/rsa2asn1 -a >key.der
; auth/secstore -G factotum | grep rsa | auth/rsa2ssh >key.pub
get those files on your unix machine.
on unix:
$ openssl rsa -inform DER -in key.der -outform PEM -out key
$ ssh-keygen -p -f key -N ''
$ echo 'whatever' | ssh-keygen -Y sign -n namespace -f key