feat(gnupg): allow gpg as ssh-agent

Deactivate regular ssh-agent in NixOS confifurations

modules/home-manager/application/gnupg/default.nix

@@ -12,14 +12,19 @@ in
       default = true;
       description = "install password-store";
     };
+
+    enableSshSupport = mkOption {
+      type = types.bool;
+      default = false;
+      description = "enable GnuPG agent SSH support";
+    };
   };
   config = mkIf cfg.enable {
 
-  home.packages = with pkgs; [
-    # pinentry-gnome
-    gcr
-  ];
-
+    home.packages = with pkgs; [
+      # pinentry-gnome
+      gcr
+    ];
     programs.gpg = {
       enable = true;
       scdaemonSettings = {
@@ -31,9 +36,17 @@ in
       enable = true;
       enableScDaemon = true;
       enableZshIntegration = true;
-      pinentry.package = pkgs.pinentry-gnome3;
+      pinentryPackage = pkgs.pinentry-gnome3;
+      enableSshSupport = cfg.enableSshSupport;
     };
 
+    home.sessionVariablesExtra = lib.mkIf cfg.enableSshSupport ''
+      if [[ -z "''${SSH_AUTH_SOCK}" ]]; then
+        export SSH_AUTH_SOCK="$(${config.programs.gpg.package}/bin/gpgconf --list-dirs agent-ssh-socket)"
+      fi
+    '';
+
+    services.ssh-agent.enable = if cfg.enableSshSupport then false else true;
     programs.password-store = {
       enable = cfg.pass;
     };