state parameter mismatch in flask application to google authentication

Question

import json
import requests
import secrets
from flask import Flask, redirect, request, session

app = Flask(__name__)
app.secret_key = 'LLL0EgZr3-0qOu6oOSWEkDQm1qht3rwBrtnyj5rPuVg'  


with open('client_secret.json') as f:
    credentials_data = json.load(f)


CLIENT_ID = credentials_data['web']['client_id']
CLIENT_SECRET = credentials_data['web']['client_secret']
REDIRECT_URI = 'http://localhost:6060/oauth2callback' 


@app.route('/authorize')
def authorize():
    state = secrets.token_urlsafe() 
    session['oauth_state'] = state  
    print(f"Stored state in session: {state}")  
    auth_url = (
        f"https://accounts.google.com/o/oauth2/auth?response_type=code&"
        f"client_id={CLIENT_ID}&redirect_uri={REDIRECT_URI}&"
        f"scope=https://www.googleapis.com/auth/drive.file&"
        f"access_type=offline&state={state}"
    )
    return redirect(auth_url)


@app.route('/oauth2callback')
def oauth2callback():
    state = request.args.get('state')
    code = request.args.get('code')


    print(f"Received state: {state}")
    print(f"Stored state: {session.get('oauth_state')}")
    

    if not state or state != session.get('oauth_state'):
        print(f"State parameter mismatch: received {state}, stored {session.get('oauth_state')}")
        return "Error: state parameter mismatch", 400

    if not code:
        return "Error: no code returned", 400

   
    token_url = "https://oauth2.googleapis.com/token"
    data = {
        'code': code,
        'client_id': CLIENT_ID,
        'client_secret': CLIENT_SECRET,
        'redirect_uri': REDIRECT_URI,
        'grant_type': 'authorization_code'
    }
    
    response = requests.post(token_url, data=data)
    token_info = response.json()

  
    if 'access_token' in token_info:
        access_token = token_info['access_token']
        return f"Access token: {access_token}"
    else:
        return f"Error retrieving access token: {token_info}", 400

if __name__ == '__main__':
    app.run(port=6060)

im trying to run this code but im getting state parameter mismatch

how do i solve this?

im trying to authorize the google authorisations

I'm building a Flask application that integrates with Google Drive using OAuth2 for authentication. The flow works fine initially, but I'm encountering an issue where the state parameter is missing from the session when redirected back from Google. This results in an error message

The problem occurs during the callback, where the state parameter seems to be missing from the session. I've checked that the session data is being set correctly before the redirection.

Questions:

1. What could be causing the state parameter to be missing from the session during the OAuth2 callback?

2. How can I ensure that the state parameter persists in the session across the OAuth2 flow?

I've ensured that the session is properly configured to use the filesystem, but the issue persists. Any insights or solutions would be greatly appreciated!

---

What I Tried:

1. Storing the state parameter in the session:

   session['state'] = state
   
   

   This is done right after generating the authorization URL in the start_authentication function.

2. Retrieving the state parameter from the session:

   state = session['state']
   
   

   This is done in the oauth2callback function to ensure the state parameter matches the one sent to Google.

What I Expected:

I expected the state parameter to be stored in the session during the initial authentication step, and then be available in the session when Google redirects back to my application after the user grants permission. This would allow me to complete the OAuth2 flow and exchange the authorization code for tokens.

What Actually Happened:

When redirected back from Google, the session does not contain the state parameter, resulting in the following error message:

{ "text": "State parameter missing in session. Please try authenticating again." }

Questions:

1. What could be causing the state parameter to be missing from the session during the OAuth2 callback?

2. How can I ensure that the state parameter persists in the session across the OAuth2 flow?

I've ensured that the session is properly configured to use the filesystem, but the issue persists. Any insights or solutions would be greatly appreciated!