Your website is vulnerable because the
SESSION_COOKIE_SECURE setting is not set - so hackers have an easier time stealing your users' session cookies on HTTP connections.
SessionMiddleware marks the session cookie as secure when
SESSION_COOKIE_SECURE = True, to make the browser only send cookie over secure HTTPS connection.
Cookies sent over insecure HTTP are unencrypted, so hackers can steal the session cookie using a packet sniffer - allowing them to effectively copy and paste it into their browser and be logged in as the user.
If our GitHub code review bot spots this issue in your pull request it gives this advice: