Google authentication MismatchingStateError in django (CSRF Warning - State not equal in request and response)

Question

I have a problem that I have been trying to resolve for the past couple of days.

When attempting to handle Google authentication in my Django web app, a MismatchingStateError is encountered at /signup/google/callback/. The issue arises when the Google authentication works correctly upon initial attempts but fails with the mentioned error after multiple tries. Even after logging in and out multiple times, the error persists.

This is my first time implementing Google authentication within Django, and I've struggled to find comprehensive guidelines or resources. I'm currently learning about flow handling and recently became aware of potential associated risks.

It's important to note that this problem resembles CSRF attacks. It emerges when there's a series of rapid login requests. After this error arises, subsequent logins are blocked. Notably, this issue isn't related to the session ID, as I've attempted to clear it without success. It seems tied to generation, possibly due to how states are managed.

See the error here

def google_auth(request):
    # Generate the Google OAuth authorization URL and redirect the user to it
    authorization_url, state = flow.authorization_url(access_type='offline', include_granted_scopes='true')
    request.session['oauth_state'] = state
    return redirect(authorization_url)

def google_callback(request):
    # Exchange the authorization code for a Google OAuth access token.
    stored_state = request.session.get('oauth_state')
    received_state = request.GET.get('state')
    
    if received_state is None or stored_state is None or received_state != stored_state:
        # State mismatch, potential CSRF attack
        return HttpResponseBadRequest("Invalid state parameter")
    
    # Clear the stored state from the session after comparing
    del request.session['oauth_state']
    
    try:
        flow.fetch_token(authorization_response=request.build_absolute_uri())
        credentials = flow.credentials
    except Exception as e:
        return render(request, 'templates/status/oauth/cooldown.html')

I've attempted to change my authorization implementation without success. Any assistance that would contribute to a solution would be greatly appreciated.

Adxzer · Accepted Answer · 2023-08-15T11:45:20.350

It proved to be a challenging task, but after some time and assistance, I successfully uncovered the solution. The primary difficulty revolved around generating the appropriate state. Rather than deriving the state from the authorization URL flow, you should generate it using the UUID library.

You can learn more about this process in this resource: How to create a GUID/UUID in Python

Here is the code:

def google_auth(request):
    new_state = str(uuid.uuid4())  # Generate a new UUID
    authorization_url, _ = flow.authorization_url(access_type='offline', include_granted_scopes='true', state=new_state)
    request.session['oauth_state'] = new_state
    return redirect(authorization_url)

def google_callback(request):
    stored_state = request.session.get('oauth_state')
    received_state = request.GET.get('state')
    if received_state is None or stored_state is None or received_state != stored_state:
        # State mismatch, potential CSRF attack
        return HttpResponseBadRequest("Invalid state parameter")
    # Clear the stored state from the session after comparing
    del request.session['oauth_state']
    try:
        flow.fetch_token(authorization_response=request.build_absolute_uri())
        credentials = flow.credentials
    except Exception as e:
        return render(request, 'templates/status/oauth/cooldown.html')

Google authentication MismatchingStateError in django (CSRF Warning - State not equal in request and response)

1 Answers1