nixpkgs/nixos/doc/manual/configuration/ssh.xml

<section xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xmlns:xi="http://www.w3.org/2001/XInclude"
         version="5.0"
         xml:id="sec-ssh">
 <title>Secure Shell Access</title>

 <para>
  Secure shell (SSH) access to your machine can be enabled by setting:
<programlisting>
<xref linkend="opt-services.openssh.enable"/> = true;
</programlisting>
  By default, root logins using a password are disallowed. They can be disabled
  entirely by setting <xref linkend="opt-services.openssh.permitRootLogin"/> to
  <literal>"no"</literal>.
 </para>

 <para>
  You can declaratively specify authorised RSA/DSA public keys for a user as
  follows:
<!-- FIXME: this might not work if the user is unmanaged. -->
<programlisting>
<link linkend="opt-users.users._name__.openssh.authorizedKeys.keys">users.users.alice.openssh.authorizedKeys.keys</link> =
  [ "ssh-dss AAAAB3NzaC1kc3MAAACBAPIkGWVEt4..." ];
</programlisting>
 </para>
</section>