The codebase that I am currently working on has a Frontend and Backend Server both making use of Flask. Now when the user login's a request is sent from the Frontend to the Backend and a session variable is set. When I use a print statement in this route I am able to see the value of the session variable. Now if the login is valid the user is directed to a landing page, here when I try to print the value of the session variable that was set in the previous route it shows up as None.

Simplified Backend Code

from flask import Flask, session
from flask_session import Session

app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret'
app.config['SESSION_TYPE'] = 'filesystem'
Session(app)

@app.route('/loginToApp', methods=["POST"])
def loginToApp(): 
    password = request.form.get('password') 
    username = request.form.get('username')

    if verifyLogin(username, password):
        session['username'] = username

    # On print session variable has the expected value
    print(session.get('username'))

    return jsonify({'username': session.get('username')})

@app.route('/landingPage', methods=["POST"])
def landingPage():
    # Value shown as None
    print(session.get('username'))

    return jsonify({'username': session.get('username')})

The /landingPage route can only be accessed using a JWT and on the Frontend I have CORS setup as well. Not sure if these the Flask Extensions that are causing the issues. Requests is used to send the requests from the Frontend to the Backend.

I am unable to figure out what I am doing wrong any and all help would be greatly appreciated.

As I understand it, sessions have to be used in flask whenever you want to work with global variables, because normal python global variables could otherwise get shared between servers or between users on the same server. I'm confused as to which variables this applies to?

If you define temporary variables within a view function - such as 'user' etc, basically anything within a def function(): - I know these don't require sessions, so I'm guessing anything defined within a view function and only used within it is fine as a standard non-session-variable. Does this mean that anything I'd define outside a view function should be a session variable? And would this also apply to a variable I define inside one view function to be used within another view function?

I know session variables can only be accessed once there is a client -> server request but I have a thread that runs concurrently outside of a request. I tried the "with app context" conditional that didn't quite work. Any ideas?