feat(nix/prog/git): add gpg key

nix/home.nix

@@ -60,6 +60,7 @@ in
       enable = true;
       inherit userName;
       inherit userEmail;
+      gpgKey = gpgSigningKey;
     };
 
     # password manager

nix/progs/git.nix

@@ -22,6 +22,12 @@ in
       type = types.str;
       description = "Set your global email";
     };
+
+    gpgKey = mkOption {
+      type = types.nullOr types.str;
+      default = null;
+      description = "The default GnuPG signing key fingerprint";
+    };
   };
   
   config = mkIf cfg.enable {
@@ -29,6 +35,10 @@ in
       enable = true;
       userName = cfg.userName;
       userEmail = cfg.userEmail;
+      signing = mkIf (cfg.gpgKey != null) {
+        key = cfg.gpgKey;
+        signByDefault = true;
+      };
       extraConfig = {
         init.defaultBranch = "main";
         pull.rebase = true;

nix/secrets.example.nix

@@ -7,5 +7,7 @@
   git = {
     userName = "Bob Ross";
     userEmail = "bross@example.com";
+    # gpg --list-secret-keys
+    gpgSigningKey = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
   };
 }