refactor: Use functional design for the authentication of apps

packages/backend/src/apps/slack2/auth/is-still-verified.ts

@@ -0,0 +1,12 @@
+import verifyCredentials from './verify-credentials';
+
+const isStillVerified = async ($: any) => {
+  try {
+    await verifyCredentials($);
+    return true;
+  } catch (error) {
+    return false;
+  }
+};
+
+export default isStillVerified;