nixos/duosec: replace insecure skey option with secure secretKeyFile option

nixos/doc/manual/release-notes/rl-2009.xml

@@ -96,6 +96,14 @@
       <option>systemd.services.supybot.serviceConfig</option>.
     </para>
    </listitem>
+   <listitem>
+    <para>
+      The <literal>security.duosec.skey</literal> option, which stored a secret in the
+      nix store, has been replaced by a new
+      <link linkend="opt-security.duosec.secretKeyFile">security.duosec.secretKeyFile</link>
+      option for better security.
+    </para>
+   </listitem>
   </itemizedlist>
  </section>
 

nixos/modules/security/duosec.nix

@@ -10,7 +10,6 @@ let
   configFilePam = ''
     [duo]
     ikey=${cfg.ikey}
-    skey=${cfg.skey}
     host=${cfg.host}
     ${optionalString (cfg.groups != "") ("groups="+cfg.groups)}
     failmode=${cfg.failmode}
@@ -24,26 +23,11 @@ let
     motd=${boolToStr cfg.motd}
     accept_env_factor=${boolToStr cfg.acceptEnvFactor}
   '';
-
-  loginCfgFile = optionalAttrs cfg.ssh.enable {
-    "duo/login_duo.conf" =
-      { source = pkgs.writeText "login_duo.conf" configFileLogin;
-        mode   = "0600";
-        user   = "sshd";
-      };
-  };
-
-  pamCfgFile = optional cfg.pam.enable {
-    "duo/pam_duo.conf" =
-      { source = pkgs.writeText "pam_duo.conf" configFilePam;
-        mode   = "0600";
-        user   = "sshd";
-      };
-  };
 in
 {
   imports = [
     (mkRenamedOptionModule [ "security" "duosec" "group" ] [ "security" "duosec" "groups" ])
+    (mkRemovedOptionModule [ "security" "duosec" "skey" ] "The insecure security.duosec.skey option has been replaced by a new security.duosec.secretKeyFile option. Use this new option to store a secure copy of your key instead.")
   ];
 
   options = {
@@ -65,9 +49,13 @@ in
         description = "Integration key.";
       };
 
-      skey = mkOption {
+      secretKeyFile = mkOption {
-        type = types.str;
+        type = types.path;
-        description = "Secret key.";
+        default = null;
+        description = ''
+          A file containing your secret key. The security of your Duo application is tied to the security of your secret key.
+        '';
+        example = "/run/keys/duo-skey";
       };
 
       host = mkOption {
@@ -198,7 +186,38 @@ in
     environment.systemPackages = [ pkgs.duo-unix ];
 
     security.wrappers.login_duo.source = "${pkgs.duo-unix.out}/bin/login_duo";
-    environment.etc = loginCfgFile // pamCfgFile;
+
+    system.activationScripts = {
+      login_duo = mkIf cfg.ssh.enable ''
+        if test -f "${cfg.secretKeyFile}"; then
+          mkdir -m 0755 -p /etc/duo
+
+          umask 0077
+          conf="$(mktemp)"
+          {
+            cat ${pkgs.writeText "login_duo.conf" configFileLogin}
+            printf 'skey = %s\n' "$(cat ${cfg.secretKeyFile})"
+          } >"$conf"
+
+          chown sshd "$conf"
+          mv -fT "$conf" /etc/duo/login_duo.conf
+        fi
+      '';
+      pam_duo = mkIf cfg.pam.enable ''
+        if test -f "${cfg.secretKeyFile}"; then
+          mkdir -m 0755 -p /etc/duo
+
+          umask 0077
+          conf="$(mktemp)"
+          {
+            cat ${pkgs.writeText "login_duo.conf" configFilePam}
+            printf 'skey = %s\n' "$(cat ${cfg.secretKeyFile})"
+          } >"$conf"
+
+          mv -fT "$conf" /etc/duo/pam_duo.conf
+        fi
+      '';
+    };
 
     /* If PAM *and* SSH are enabled, then don't do anything special.
     If PAM isn't used, set the default SSH-only options. */