Migrate to Snowfall (#1)

Reviewed-on: #1
Co-authored-by: Evan Reichard <evan@reichard.io>
Co-committed-by: Evan Reichard <evan@reichard.io>

modules/nixos/services/openssh/default.nix

@@ -0,0 +1,80 @@
+{ config, lib, namespace, ... }:
+let
+  inherit (lib)
+    types
+    mkDefault
+    mkIf
+    ;
+  inherit (lib.${namespace}) mkOpt;
+
+  cfg = config.${namespace}.services.openssh;
+
+  authorizedKeys = [
+    # evanreichard@lin-va-mbp-personal
+    "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILJJoyXQOv9cAjGUHrUcvsW7vY9W0PmuPMQSI9AMZvNY"
+    # evanreichard@lin-va-thinkpad
+    "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAq5JQr/6WJMIHhR434nK95FrDmf2ApW2Ahd2+cBKwDz"
+  ];
+in
+{
+  options.${namespace}.services.openssh = with types; {
+    enable = lib.mkEnableOption "OpenSSH support";
+    authorizedKeys = mkOpt (listOf str) authorizedKeys "The public keys to apply.";
+    extraConfig = mkOpt str "" "Extra configuration to apply.";
+  };
+
+  config = mkIf cfg.enable {
+    services.openssh = {
+      enable = true;
+
+      hostKeys = mkDefault [
+        {
+          bits = 4096;
+          path = "/etc/ssh/ssh_host_ed25519_key";
+          type = "ed25519";
+        }
+      ];
+
+      openFirewall = true;
+      ports = [ 22 ];
+
+      settings = {
+        AuthenticationMethods = "publickey";
+        ChallengeResponseAuthentication = "no";
+        PasswordAuthentication = false;
+        PermitRootLogin = "prohibit-password";
+        PubkeyAuthentication = "yes";
+        StreamLocalBindUnlink = "yes";
+        UseDns = false;
+        UsePAM = true;
+        X11Forwarding = false;
+
+        KexAlgorithms = [
+          "curve25519-sha256"
+          "curve25519-sha256@libssh.org"
+          "diffie-hellman-group16-sha512"
+          "diffie-hellman-group18-sha512"
+          "diffie-hellman-group-exchange-sha256"
+          "sntrup761x25519-sha512@openssh.com"
+        ];
+
+        Macs = [
+          "hmac-sha2-512-etm@openssh.com"
+          "hmac-sha2-256-etm@openssh.com"
+          "umac-128-etm@openssh.com"
+        ];
+      };
+
+      startWhenNeeded = true;
+    };
+
+    programs.ssh = {
+      startAgent = lib.mkDefault true;
+      inherit (cfg) extraConfig;
+    };
+
+    reichard = {
+      user.extraOptions.openssh.authorizedKeys.keys = cfg.authorizedKeys;
+    };
+  };
+}