before_first_request has been deprecated

When running `flask run`, an error will occur: `AttributeError: 'Flask' object has no attribute 'before_first_request'`.

workaround: 

```diff
diff --git a/requirements.txt b/requirements.txt
index a9a0f2d..34f5e84 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,3 @@
-Flask
+Flask~=2.2.0
 Flask-SQLAlchemy
 Authlib
```