I tried implementing the basic authentication in Apache on my Flask app. I did it via the host config, but the authentication popup is not showing up, it just works like normal.

<VirtualHost *:80>
    ServerName monitor.domain.com
    DocumentRoot /home/ubuntu/monitor/

    WSGIDaemonProcess app user=www-data group=www-data threads=5 python-home=/home/ubuntu/monitor/venv
    WSGIScriptAlias / /home/ubuntu/monitor/flask-app.wsgi

    ErrorLog ${APACHE_LOG_DIR}/flask-error.log
    CustomLog ${APACHE_LOG_DIR}/flask-access.log combined

    <Directory /home/ubuntu/monitor>
            AuthType Basic
            AuthName "Restricted Access"
            AuthUserFile /etc/apache2/.htpasswd
            Require valid-user
            WSGIProcessGroup app
            WSGIApplicationGroup %{GLOBAL}
            #Order deny,allow
            #Require all granted
    </Directory>

    RewriteEngine on
    RewriteCond %{SERVER_NAME} =monitor.domain.com
    RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]

The .htpasswd already contains something:

myuser:$apr1$0glFoCsO$u62LjHvLMQznQqv..K63A0