bekkalokk: set up kerberos client

hosts/bekkalokk/services/kerberos/krb5.nix

@@ -0,0 +1,90 @@
+{ config, lib, pkgs, ... }:
+let
+  inherit (lib) mdDoc mkIf mkOption mkPackageOption mkRemovedOptionModule;
+  inherit (lib.types) bool;
+
+  mkRemovedOptionModule' = name: reason: mkRemovedOptionModule ["krb5" name] reason;
+  mkRemovedOptionModuleCfg = name: mkRemovedOptionModule' name ''
+    The option `krb5.${name}' has been removed. Use
+    `security.krb5.settings.${name}' for structured configuration.
+  '';
+
+  cfg = config.security.krb5;
+  format = import ./krb5-conf-format.nix { inherit pkgs lib; } { };
+in {
+  imports = [
+    (mkRemovedOptionModuleCfg "libdefaults")
+    (mkRemovedOptionModuleCfg "realms")
+    (mkRemovedOptionModuleCfg "domain_realm")
+    (mkRemovedOptionModuleCfg "capaths")
+    (mkRemovedOptionModuleCfg "appdefaults")
+    (mkRemovedOptionModuleCfg "plugins")
+    (mkRemovedOptionModuleCfg "config")
+    (mkRemovedOptionModuleCfg "extraConfig")
+    (mkRemovedOptionModule' "kerberos" ''
+      The option `krb5.kerberos' has been moved to `security.krb5.package'.
+    '')
+  ];
+
+  options = {
+    security.krb5 = {
+      enable = mkOption {
+        default = false;
+        description = mdDoc "Enable and configure Kerberos utilities";
+        type = bool;
+      };
+
+      package = mkPackageOption pkgs "krb5" {
+        example = "heimdal";
+      };
+
+      settings = mkOption {
+        default = { };
+        type = format.type;
+        description = mdDoc ''
+          Structured contents of the {file}`krb5.conf` file. See
+          {manpage}`krb5.conf(5)` for details about configuration.
+        '';
+        example = {
+          include = [ "/run/secrets/secret-krb5.conf" ];
+          includedir = [ "/run/secrets/secret-krb5.conf.d" ];
+
+          libdefaults = {
+            default_realm = "ATHENA.MIT.EDU";
+          };
+
+          realms = {
+            "ATHENA.MIT.EDU" = {
+              admin_server = "athena.mit.edu";
+              kdc = [
+                "athena01.mit.edu"
+                "athena02.mit.edu"
+              ];
+            };
+          };
+
+          domain_realm = {
+            "mit.edu" = "ATHENA.MIT.EDU";
+          };
+
+          logging = {
+            kdc = "SYSLOG:NOTICE";
+            admin_server = "SYSLOG:NOTICE";
+            default = "SYSLOG:NOTICE";
+          };
+        };
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    environment = {
+      systemPackages = [ cfg.package ];
+      etc."krb5.conf".source = format.generate "krb5.conf" cfg.settings;
+    };
+  };
+
+  meta.maintainers = builtins.attrValues {
+    inherit (lib.maintainers) dblsaiko h7x4;
+  };
+}