Add oauth route api checks

src/routes/oauth/OAuthRoute.svelte

@@ -0,0 +1,23 @@
+<script lang="ts">
+  import { onMount } from "svelte";
+  import { navigate, useLocation } from "svelte-navigator";
+  import { getUser } from "~/api/login";
+
+  let location = useLocation();
+
+  onMount(async () => {
+    try {
+      await getUser("@me");
+    } catch (_) {
+      let params = new URLSearchParams();
+      params.set("back", window.location.pathname + window.location.search);
+      navigate("/login" + params.toString());
+    }
+    try {
+      let params = new URLSearchParams($location.search);
+      await getOAuthApp(params.get("client_id"));
+    } catch (_) {
+      navigate("/oauth/invalid-app");
+    }
+  });
+</script>