AuthProxy: Fix unauthenticated request handler logic

Change-Id: I931546846b46e5418eb08f2b39fb3149cfda13d4
diff --git a/core/auth/proxy/main.go b/core/auth/proxy/main.go
index 8c98d20..adf789c 100644
--- a/core/auth/proxy/main.go
+++ b/core/auth/proxy/main.go
@@ -147,8 +147,13 @@
 	}
 	fmt.Printf("%+v\n", user)
 	rc := r.Clone(context.Background())
-	rc.Header.Add("X-Forwarded-User", user.Identity.Traits.Username)
-	rc.Header.Add("X-Forwarded-UserId", user.Identity.Id)
+	if user != nil {
+		rc.Header.Add("X-Forwarded-User", user.Identity.Traits.Username)
+		rc.Header.Add("X-Forwarded-UserId", user.Identity.Id)
+	} else {
+		delete(rc.Header, "X-Forwarded-User")
+		delete(rc.Header, "X-Forwarded-UserId")
+	}
 	ru, err := url.Parse(fmt.Sprintf("http://%s%s", *upstream, r.URL.RequestURI()))
 	if err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)