pam: switch to using sudo_local file

modules/security/pam.nix

@@ -2,66 +2,63 @@
 
 let
   cfg = config.security.pam;
-
-  # Implementation Notes
-  #
-  # We don't use `environment.etc` because this would require that the user manually delete
-  # `/etc/pam.d/sudo` which seems unwise given that applying the nix-darwin configuration requires
-  # sudo. We also can't use `system.patchs` since it only runs once, and so won't patch in the
-  # changes again after OS updates (which remove modifications to this file).
-  #
-  # As such, we resort to line addition/deletion in place using `sed`. We add a comment to the
-  # added line that includes the name of the option, to make it easier to identify the line that
-  # should be deleted when the option is disabled.
-  mkSudoTouchIdAuthScript = isEnabled:
-  let
-    file   = "/etc/pam.d/sudo";
-    option = "security.pam.enableSudoTouchIdAuth";
-    sed = "${pkgs.gnused}/bin/sed";
-  in ''
-    ${if isEnabled then ''
-      # Enable sudo Touch ID authentication, if not already enabled
-      if ! grep 'pam_tid.so' ${file} > /dev/null; then
-        ${sed} -i '2i\
-      auth       sufficient     pam_tid.so # nix-darwin: ${option}
-        ' ${file}
-      fi
-    '' else ''
-      # Disable sudo Touch ID authentication, if added by nix-darwin
-      if grep '${option}' ${file} > /dev/null; then
-        ${sed} -i '/${option}/d' ${file}
-      fi
-    ''}
-  '';
 in
-
 {
   options = {
-    security.pam.enableSudoTouchIdAuth = lib.mkEnableOption "" // {
-      description = ''
-        Enable sudo authentication with Touch ID.
-
-        When enabled, this option adds the following line to
-        {file}`/etc/pam.d/sudo`:
+    security.pam = {
+      enable = lib.mkEnableOption "managing PAM with nix-darwin" // {
+        default = true;
+        example = false;
+      };
 
-        ```
-        auth       sufficient     pam_tid.so
-        ```
+      enableSudoTouchIdAuth = lib.mkEnableOption "" // {
+        description = ''
+          Whether to enable Touch ID with sudo.
 
-        ::: {.note}
-        macOS resets this file when doing a system update. As such, sudo
-        authentication with Touch ID won't work after a system update
-        until the nix-darwin configuration is reapplied.
-        :::
-      '';
+          This will also allow your Apple Watch to be used for sudo. If this doesn't work,
+          you can go into `System Settings > Touch ID & Password` and toggle the switch for
+          your Apple Watch.
+        '';
+      };
     };
   };
 
   config = {
-    system.activationScripts.pam.text = ''
+    environment.etc."pam.d/sudo_local" = {
+      inherit (cfg) enable;
+      text = lib.optionalString cfg.enableSudoTouchIdAuth "auth       sufficient     pam_tid.so";
+    };
+
+    system.activationScripts.pam.text =
+    let
+      file = "/etc/pam.d/sudo";
+      marker = "security.pam.sudo_local";
+      deprecatedOption = "security.pam.enableSudoTouchIdAuth";
+      sed = lib.getExe pkgs.gnused;
+    in
+    ''
       # PAM settings
       echo >&2 "setting up pam..."
-      ${mkSudoTouchIdAuthScript cfg.enableSudoTouchIdAuth}
+
+      # REMOVEME when macOS 13 no longer supported as macOS automatically
+      # nukes this file on system upgrade
+      # Always clear out older implementation if it is present
+      if grep '${deprecatedOption}' ${file} > /dev/null; then
+        ${sed} -i '/${deprecatedOption}/d' ${file}
+      fi
+
+      ${if cfg.enable then ''
+        # REMOVEME when macOS 13 no longer supported
+        # `sudo_local` is automatically included after macOS 14
+        if ! grep 'sudo_local' ${file} > /dev/null; then
+          ${sed} -i '2iauth       include        sudo_local # nix-darwin: ${marker}' ${file}
+        fi
+      '' else ''
+        # Remove include line if we added it
+        if grep '${marker}' ${file} > /dev/null; then
+          ${sed} -i '/${marker}/d' ${file}
+        fi
+      ''}
     '';
   };
 }