If trying to connect with Notepad++ to an OS X El Capitain ssh default server, you get the error:
[SFTP] None of the server's authentication methods were accepted. Please check the options under the authentication tab.
you could edit your connection’s settings to use keyboard interactive authentication, instead of password authentication:
Profile settings > Select the desired connection > Authentication > Check “Try keyboard interactive authentication”
More info here:
The starting point for another aproach can be found withing the following two links:
http://serverfault.com/questions/85992/how-do-i-setup-sshd-on-mac-os-x-to-only-allow-key-based-authentication
http://superuser.com/questions/364304/how-do-i-configure-ssh-on-os-x