nix read user keys

users.nix

{ config, pkgs, ... }:

{  
  ##
  ## User management
  ##
  users.users =
    let loadUserConfiguration = userName:
      # set structure chosen to fit the builtins.listToAttrs
      {
        name = userName;
        value = {
          openssh = {
            authorizedKeys = {
               keyFiles =
                let verifyKeyFile = fileName:
                  if (builtins.substring ((builtins.stringLength fileName) - 3) 3 fileName) == "pub" then (./users/- + userName + "-/-" + (builtins.substring 1 ((builtins.stringLength fileName) - 1) fileName)) else "";
                in map verifyKeyFile (builtins.attrNames (builtins.readDir (./users/- + userName + "-")));
            };
         };
       };
     };
   # read the user directory; map it to a substring removing the trailing and leading "-" dash; map it to the above declared function; convert the list to a set
   in builtins.listToAttrs (map loadUserConfiguration (map (userName: builtins.substring 1 ((builtins.stringLength userName) - 2) userName) (builtins.attrNames (builtins.readDir ./users))));
}