PrivateNetwork: Configure cluster proxy backend

Change-Id: Ieeca2da6bd69ee3a440960ff3d4cdb9371f3a8c6
diff --git a/core/headscale/main.go b/core/headscale/main.go
index c2cfcf5..d4a129f 100644
--- a/core/headscale/main.go
+++ b/core/headscale/main.go
@@ -131,7 +131,7 @@
 		http.Error(w, err.Error(), http.StatusBadRequest)
 		return
 	}
-	if err := s.client.createUser(req.Name); err != nil {
+	if err := s.client.createUser(req.Name); err != nil && !errors.Is(err, ErrorAlreadyExists) {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}