fix OAuth2 issue

src/App.js

@@ -4,6 +4,7 @@ import MainNavigation from "./components/MainNavigation";
 import SideNavigation from "./components/SideNavigation";
 import MarkdownContent from "./components/MarkdownContent";
 import "./App.css";
+import Callback from "./Callback";
 
 const App = () => {
     return (
@@ -16,6 +17,8 @@ const App = () => {
                         <Routes>
                             <Route path="/" element={<h1>Welcome to My React Project</h1>} />
                             <Route path="/markdown/:id" element={<MarkdownContent />} />
+                            <Route path="/callback" element={<Callback />} />
+                            <Route path="/test" element={<h1>TEST</h1>}></Route>
                         </Routes>
                     </main>
                 </div>