freeradius: make debug logging optional

(cherry picked from commit 0587329)

nixos/modules/services/networking/freeradius.nix

@@ -17,7 +17,8 @@ let
     '';
 
     serviceConfig = {
-        ExecStart = "${pkgs.freeradius}/bin/radiusd -f -d ${cfg.configDir} -l stdout -xx";
+        ExecStart = "${pkgs.freeradius}/bin/radiusd -f -d ${cfg.configDir} -l stdout" +
+                    optionalString cfg.debug " -xx";
         ExecReload = [
           "${pkgs.freeradius}/bin/radiusd -C -d ${cfg.configDir} -l stdout"
           "${pkgs.coreutils}/bin/kill -HUP $MAINPID"
@@ -41,6 +42,16 @@ let
       '';
     };
 
+    debug = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Whether to enable debug logging for freeradius (-xx
+        option). This should not be left on, since it includes
+        sensitive data such as passwords in the logs.
+      '';
+    };
+
   };
 
 in
@@ -66,6 +77,7 @@ in
     };
 
     systemd.services.freeradius = freeradiusService cfg;
+    warnings = optional cfg.debug "Freeradius debug logging is enabled. This will log passwords in plaintext to the journal!";
 
   };