Resetting the expiration time for a cookie in Flask

Should be enough with:

from datetime import timedelta

# User will be logout after this time of inactivity
PERMANENT_SESSION_LIFETIME = timedelta(minutes=30)
SESSION_REFRESH_EACH_REQUEST = True

https://flask.palletsprojects.com/en/1.1.x/config/

You can renew the session to the client at each request using a @before_request handler.

Try the following:

@app.before_request
def func():
  session.modified = True