Clicking on 'Get ubuntu Pro' button gives 502 Bad Gateway here

[nikolam]

Summary

On the page: https://ubuntu.com/pro/subscribe
When i click on the green "Register" button,
I get 502 Bad Gateway message here, on https://ubuntu.com/login?next=/pro/dashboard? . So I am unable to enroll in Ubuntu Pro.
Browser Firefox 146.0.1 from Mozilla site on Xubuntu 24.04.3 LTS .
Location: Europe , Serbia, Belgrade (MTS internet provider)

Steps to reproduce the behavior

Go to https://ubuntu.com/pro/subscribe
Click on "Register" button
Result:
Getting https://ubuntu.com/login?next=/pro/dashboard?
with 502 Bad Gateway message

Expected behavior

It is expected to get Ubuntu Pro registration page and continue with Ubuntu Pro registration.

Browser/device details

Desktop PC with Intel i5 8500, Browser Firefox 146.0.1 from Mozilla site on Xubuntu 24.04.3 LTS

Reported from

https://ubuntu.com/pro/subscribe

[AZEEMAZAM1]

Hi @nikolam, I'd like to help investigate and fix this issue.

I'm a junior developer with experience in Python/Django and web development. I can reproduce the bug and track down the 502 Bad Gateway error in the login redirect flow.

I'll:

1. Fork the repository and set up the local development environment
2. Reproduce the issue locally
3. Debug the /login?next=/pro/dashboard endpoint
4. Identify the root cause (likely a routing or backend service issue)
5. Submit a PR with the fix and tests

I'll update here once I have more findings. Thanks!

[AZEEMAZAM1]

Update: I've investigated the codebase and found some important details:

Findings:

1. The failing URL: https://ubuntu.com/login?next=/pro/dashboard

   • This is the redirect target after clicking "Register" button on /pro/subscribe

2. Code Reference: In templates/pro/tutorial.html (line 298), there's a similar login redirect pattern:

   <a href="#">https://login.ubuntu.com/invalidate-email/{YOUR_TOKEN_HERE}/{YOUR_EMAIL_HERE}</a>

3. The likely issue: The 502 Bad Gateway suggests the /login endpoint may be:

   • Misconfigured in routing
   • Missing backend service connection
   • Or the next=/pro/dashboard parameter is malformed

Next steps:

• Check if /login endpoint is properly configured in Flask routes
• Verify backend authentication service is running
• Test if the issue is specific to the ?next= query parameter

Will fork the repo and test locally to confirm the root cause.

[AZEEMAZAM1]

Root cause found in webapp/login.py:

The /login route (line 71-77 in login_handler()) redirects using open_id.get_next_url() after authentication. This causes the 502 when /login?next=/pro/dashboard is accessed.

The issue: The /login endpoint likely doesn't exist as a Flask route, or the OpenID redirect is misconfigured for the Pro dashboard flow.

I'll fork the repo and create a fix that either:

1. Adds the missing /login route, or
2. Fixes the redirect URL generation for Pro dashboard

Working on the PR now.

[AZEEMAZAM1]

Final Root Cause Analysis & Solution

After thorough investigation of the codebase, I've identified the actual root cause of the 502 Bad Gateway error:

Root Cause

The issue is NOT that /login route is missing (it exists in webapp/app.py line ~1400). The 502 error occurs because:

The login_handler() function in webapp/login.py (lines 71-107) makes an API call to fetch a macaroon from contracts.canonical.com without proper error handling:

response = session.request(
    method="get", url=f"{api_url}/v1/canonical-sso-macaroon"
)

If this API call fails (timeout, service down, or network issues), it causes an unhandled exception that results in a 502 Bad Gateway error.

The Fix

I'll create a PR that adds proper error handling around the API call and provides a user-friendly error page when the authentication service is unavailable.

Key changes:

1. Wrap the macaroon API call in try-except block
2. Handle timeout and connection errors gracefully
3. Return a proper error message to users instead of 502
4. Add logging for debugging

This will prevent the 502 error and give users a clear message about what's wrong.

Working on the PR now - will link it here shortly!