nixpkgs/nixos/doc/manual/configuration/wireless.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-wireless">

<title>Wireless Networks</title>

<para>For a desktop installation using NetworkManager (e.g., GNOME),
you just have to make sure the user is in the
<code>networkmanager</code> group and you can skip the rest of this
section on wireless networks.</para>

<para>
NixOS will start wpa_supplicant for you if you enable this setting:

<programlisting>
networking.wireless.enable = true;
</programlisting>

NixOS lets you specify networks for wpa_supplicant declaratively:
<programlisting>
networking.wireless.networks = {
  echelon = {
    psk = "abcdefgh";
  };
  "free.wifi" = {};
}
</programlisting>

Be aware that keys will be written to the nix store in plaintext!

When no networks are set, it will default to using a configuration file at
<literal>/etc/wpa_supplicant.conf</literal>. You should edit this file
yourself to define wireless networks, WPA keys and so on (see
wpa_supplicant.conf(5)).
</para>

<para>
If you are using WPA2 the <command>wpa_passphrase</command> tool might be useful
to generate the <literal>wpa_supplicant.conf</literal>.

<screen>
# wpa_passphrase ESSID PSK > /etc/wpa_supplicant.conf</screen>

After you have edited the <literal>wpa_supplicant.conf</literal>,
you need to restart the wpa_supplicant service.

<screen>
# systemctl restart wpa_supplicant.service</screen>
</para>

</section>