BasicAuthentication does not work for me

Dash Python
1

I followed the examples to create a sinple Basic Authenticaiton and have this sample prog:

import dash
import dash_html_components as html
import dash_auth

#user dictionary
USERNAME_PASSWORD_PAIRS = {
     'user1': 'pw1','user2': 'pw2'
}

external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']

app = dash.Dash(__name__, external_stylesheets=external_stylesheets)
auth = dash_auth.BasicAuth(
    app,
    USERNAME_PASSWORD_PAIRS
)

app.layout=html.P(' test page')

if __name__ == '__main__':
    app.run_server(debug=True)

nevertheless when I run it it asks user/pwd but remains there after providing the right pwd and does not show the page.

Can someone help ?

thanks
Alessandro