feat(lib): Declare instance specific function here instead of nix-lib

lib/default.nix

@@ -1,9 +1,23 @@
 _:
 
 let
+  sources = import ../npins;
+
+  nix-lib = import sources.nix-lib {
     inherit ((import sources.nixpkgs { })) lib;
 
-  sources = import ../npins;
-in
+    keysRoot = ../keys;
+    metaRoot = ../meta;
+  };
 
-import sources.nix-lib { inherit lib; keysRoot = ../keys; metaRoot = ../meta; }
+in nix-lib // (with nix-lib; {
+  # Get publickeys associated to a node
+  getNodeKeys = node:
+    let
+      meta = import ../meta;
+      names =
+        builtins.foldl' (names: group: names ++ meta.members.groups.${group})
+        (meta.nodes.${node}.admins ++ [ "/machines/${node}" ])
+        (meta.nodes.${node}.adminGroups ++ [ "root" ]);
+    in getAllKeys names;
+})