multiple user-session managemnet - session

Question

im trying to build an flask application with user authentication. each user has different pages to be shown. the issue im facing is whenever user A logs in his username is saved in session variable and i use this to prevent users toggling through url without logging in first. but whenever user B logs in,user A is able to see what user B can. the previous session data is being over written. it would amazing if anyone can let me know how do i declare another session each time a new user walks in.
from flask import Flask,render_template,redirect,session,request,g,make_response,url_for
import psycopg2
import os
appt = Flask(__name__)
appt.secret_key= os.urandom(16)
conn=psycopg2.connect( database="one",user="postgres",password="0000",host="localhost",port="5432" )
cursor = conn.cursor()
cursor.execute("select username from use")
us=cursor.fetchall()
cursor.execute("select password from use")
psw= cursor.fetchall()
i use the above database data for user authentication
#appt.route('/',methods=['GET','POST'])
def index():
if request.method=='POST':
global user_name
user_name=request.form['username'] # make it global
pass_word=request.form['password']
for i in range(len(us)):
if user_name in us[i][0]:
new=psw[i][0]
if new==pass_word:
print(session.get('user'))
if 'user' not in session:
print('new user')
user = request.form['username'] # setting user to cookie with userid: username
resp = make_response(render_template('monitor.html'))
resp.set_cookie('userID', user) # setting a cookie
print(request.cookies.get('userID'))
return resp
else:
print('old user')
return session.get('user')
else:
return render_template('login.html',info="invalid user")
return render_template('login.html')
#appt.route('/logout', methods=['GET', 'POST'])
def logout():
print("hello")
if g.user:
if request.method == 'GET':
print("hello")
print(session['user'][0])
session.pop('user',None)
return render_template("login.html")
else:
return redirect("monitor.html")
#appt.before_request
def before_request():
#g.user=None
if 'user' in session:
g.user = session['user']
if __name__ == '__main__':
appt.run(debug=True)