modules: add secrets/age.nix

modules/secrets/age.nix

@@ -0,0 +1,93 @@
+{ config, pkgs, lib, ... }:
+
+with lib;
+let
+  options.nix-bitcoin.age = {
+    enable = mkOption {
+      type = types.bool;
+      default = false;
+      description = mdDoc ''
+        Enable age-encrypted secrets.
+
+        This requires that the [agenix](https://github.com/ryantm/agenix)
+        module is included in your config.
+      '';
+    };
+
+    secretsSourceDir = mkOption {
+      type = types.path;
+      example = literalExpression "./secrets";
+      description = mdDoc ''
+        The directory where age-encrypted secrets are stored.
+      '';
+    };
+
+    publicKeys = mkOption {
+      type = with types; listOf str;
+      example = [ "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIL0idNvgGiucWgup/mP78zyC23uFjYq0evcWdjGQUaBH" ];
+      description = mdDoc ''
+        Public keys for encrypting the secrets.
+
+        A sensible default is to set this to the ed25519 public SSH host key of your node.
+        You can query host keys with command {command}`ssh-keyscan <node address>`.
+
+        When not using a SSH host key, make sure to set the corresponding agenix
+        option {option}`age.identityPaths`.
+      '';
+    };
+
+    generateSecretsScript = mkOption {
+      readOnly = true;
+
+      description = mdDoc secretsScriptLib.scriptHelp;
+
+      default = pkgs.writers.writeBashBin "generate-secrets" ''
+        ${secretsScriptLib.gotoDestDir}
+
+        tmpSecretsDir=$(mktemp -d)
+        trap 'rm -rf $tmpSecretsDir' EXIT
+
+        # 1. Generate secrets to a tmp dir
+        pushd "$tmpSecretsDir" >/dev/null
+        ${config.nix-bitcoin.generateSecretsScriptImpl}
+        popd >/dev/null
+
+        # 2. Age-encrypt each secret to $PWD/$name.age
+        encrypt() {
+          ${getExe pkgs.rage} "$tmpSecretsDir/$1" -o "$1.age" ${
+            concatMapStringsSep " " (pubkey:
+              "--recipient ${escapeShellArg pubkey}"
+            ) cfg.publicKeys
+          }
+        }
+        ${
+          concatMapStrings (name: ''
+            encrypt "${name}"
+          '') (builtins.attrNames config.nix-bitcoin.secrets)
+        }
+      '';
+    };
+  };
+
+  cfg = config.nix-bitcoin.age;
+  inherit (config.nix-bitcoin) secretsScriptLib;
+in {
+  inherit options;
+
+  config = {
+    nix-bitcoin.secretsSetupMethod = "age";
+
+    nix-bitcoin.secretsDir = config.age.secretsDir;
+
+    # The `nix-bitcoin-secrets` target has no dependencies,
+    # because agenix runs via the activation script, before systemd.
+    systemd.targets.nix-bitcoin-secrets = {};
+
+    age.secrets = mapAttrs (name: value: {
+      owner = value.user;
+      group = value.group;
+      mode = value.permissions;
+      file = (cfg.secretsSourceDir + "/${name}.age");
+    }) config.nix-bitcoin.secrets;
+  };
+}