By default, the session domain should be the SERVER_NAME of your Flask app. For example, if you website domain is example.com then the session domain should be example.com which you can see in Edge at edge://settings/content/cookies/siteData.
SESSION_COOKIE_DOMAIN can be set in __init__.py. In this example, the session domain is set to 127.0.0.1, the hostname when running Flask in VSCode.
from flask import Flask
from datetime import timedelta
def myapp():
app = Flask(__name__)
app.config['SECRET_KEY'] = "akDFJ34mdfsYMH567sdf" # this must be set in order to use sessions
app.config['SESSION_COOKIE_DOMAIN'] = '127.0.0.1'
return app
You may want to also run Flask in debug mode so you get additional logging to better understand what Flask is doing.
from myapp import app
app = app()
if __name__ == "__main__":
app.run(debug=True)
