Generate ssh-key if none available

home-manager.nix

@@ -1,6 +1,8 @@
 { config, pkgs, lib, ... }:
 let
     profile = import ./profile.nix;
+    home-directory = "/home/${profile.username}";
+    ssh-filename = "${home-directory}/.ssh/id_ed25519";
 in
 {
 
@@ -37,4 +39,22 @@ in
             };
         };
     };
+
+    systemd.services.generate-ssh-key = {
+    	description = "Generate SSH key if missing";
+    	wantedBy = [ "multi-user.target" ];
+    	after = [ "network.target" ];
+    	serviceConfig = {
+		Type = "oneshot";
+      		User = user;
+    };
+
+    script = ''
+      if [ ! -f ${ssh-filename} ]; then
+        mkdir -p ${home-directory}/.ssh
+        chmod 700 ${home-directory}/.ssh
+        ${pkgs.openssh}/bin/ssh-keygen -t ed25519 -N "" -f ${ssh-filename}
+      fi
+    '';
+  };
 }