nixos/synergy: add encryption support

Make it possible to use the Synergy server with TLS encryption without
resorting to the GUI.

nixos/modules/services/misc/synergy.nix

@@ -70,6 +70,26 @@ in
           type = types.bool;
           description = "Whether the Synergy server should be started automatically.";
         };
+        tls = {
+          enable = mkOption {
+            type = types.bool;
+            default = false;
+            description = ''
+              Whether TLS encryption should be used.
+
+              Using this requires a TLS certificate that can be
+              generated by starting the Synergy GUI once and entering
+              a valid product key.
+            '';
+          };
+
+          cert = mkOption {
+            type = types.nullOr types.str;
+            default = null;
+            example = "~/.synergy/SSL/Synergy.pem";
+            description = "The TLS certificate to use for encryption.";
+          };
+        };
       };
     };
 
@@ -95,7 +115,7 @@ in
         description = "Synergy server";
         wantedBy = optional cfgS.autoStart "graphical-session.target";
         path = [ pkgs.synergy ];
-        serviceConfig.ExecStart = ''${pkgs.synergy}/bin/synergys -c ${cfgS.configFile} -f ${optionalString (cfgS.address != "") "-a ${cfgS.address}"} ${optionalString (cfgS.screenName != "") "-n ${cfgS.screenName}" }'';
+        serviceConfig.ExecStart = ''${pkgs.synergy}/bin/synergys -c ${cfgS.configFile} -f${optionalString (cfgS.address != "") " -a ${cfgS.address}"}${optionalString (cfgS.screenName != "") " -n ${cfgS.screenName}"}${optionalString cfgS.tls.enable " --enable-crypto"}${optionalString (cfgS.tls.cert != null) (" --tls-cert=${cfgS.tls.cert}")}'';
         serviceConfig.Restart = "on-failure";
       };
     })