`routes_pathname_prefix` not respected for route authorization

Hi!

The `routes_pathname_prefix` is not respected in the following which breaks public routes and callbacks if a prefix is used:

https://github.com/plotly/dash-auth/blob/18f66d308943c8bda792e22d3e697414cd36a1c3/dash_auth/auth.py#L57

edit: Maybe this could be an alternative?

```python
if request.url_rule and app.server.view_functions.get(request.url_rule.endpoint) == app.dispatch:
```