nix-daemon: Add trusted-users and allowed-users options

‘trusted-users’ is a list of users and groups that have elevated
rights, such as the ability to specify binary caches. It defaults to
‘root’. A typical value would be ‘@wheel’ to specify all users in the
wheel group.

‘allowed-users’ is a list of users and groups that are allowed to
connect to the daemon. It defaults to ‘*’. A typical value would be
‘@users’ to specify the ‘users’ group.

src/libstore/globals.hh

@@ -203,6 +203,15 @@ struct Settings {
     /* Whether the importNative primop should be enabled */
     bool enableImportNative;
 
+    /* List of users that have elevated rights in the Nix daemon, such
+       as the ability to specify additional binary caches, or to
+       import unsigned NARs. */
+    Strings trustedUsers;
+
+    /* List of users that are allowed to connect to the daemon, in
+       addition to the trusted users. These have normal rights. */
+    Strings allowedUsers;
+
 private:
     SettingsMap settings, overrides;