use ssh keys instead of password

lib/helpers.nix

@@ -0,0 +1,18 @@
+{ lib, ... }:
+
+with lib;
+rec {
+  indexFrom = origin: name: item: list: foldr
+  (h: t:
+    if h.${origin} == name && hasAttr item h
+    then h.${item}
+    else t)
+  (error ''
+    No item at the origin point ${origin} with element ${name} found.
+    Please make sure that the item with that origin exists, and,
+    failing that, that it also has the requested item defined.
+  '')
+  list;
+
+  getSSH = name: keys: indexFrom "hostname" name "ssh" keys;
+}