ssh-copy-idで公開鍵を渡す - Qiita

$ ssh-copy-id -i ~/.ssh/id_ed25519_lan.pub pi@192.168.2.50
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/Users/username/.ssh/id_ed25519_lan.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
pi@192.168.2.50's password:

Number of key(s) added:        1

Now try logging into the machine, with:   "ssh 'pi@192.168.2.50'"
and check to make sure that only the key(s) you wanted were added.

注意 ユーザのパスワード認証は求められる。ユーザにパスワードを設定していない場合でも。

ssh-copy-id で行なっているのは security - ssh-copy-id without authentication - Ask Ubuntu

scp ~/.ssh/id_ed25519_lan.pub pi@192.168.2.50:
ssh pi@192.168.2.50 'cat id_rsa.pub >> .ssh/authorized_keys'
ssh pi@192.168.2.50 'rm ~/.ssh/id_ed25519_lan.pub'