Add migration error for candid creds

Metadata

Project: snapcraft
Number: #6414
Type: issue
State: open
Author: mr-cal
Labels: Status: Triaged Type: Enhancement
Created: 2026-09-04 12:29 PM UTC
Updated: 2026-09-08 06:41 PM UTC
Closed: —

Current evaluation

Enhancement to detect candid credentials in creds files and raise a user-friendly migration error, complementing existing env var checks.

Suggested action: keep open

Reason: This is a triaged enhancement (Status: Triaged label present) that is clearly scoped: detect candid credentials in creds files and raise a migration error. The existing code in snapcraft/commands/account.py already checks SNAPCRAFT_STORE_AUTH=candid for login/export-login commands, but the issue specifically requests also parsing the creds file to detect candid credentials stored there. It was opened 4 days ago by a maintainer and is ready for implementation.

Impact: 55 Quick Win: 35.75 Staleness: 0 Complexity: 35 Confidence: 75 Support Request: 10

Issue body

### Check existing issues - [x] I've verified that this request isn't described by any existing issues. ### Request Snapcraft 9.1 removed Candid as a valid authentication method. However, we need to detect candid credentials and raise a user-friendly error. We can do this by checking if `SNAPCRAFT_STORE_AUTH=candid` is set and/or by parsing the creds file (candid creds are easy to classify). ### The problem it solves It gives users a clear error message, so they aren't confused when Snapcraft 9.1 stops accepting their auth.

Evaluation history

Date	Model	Scores	Action	Summary
2026-09-08 06:50 PM UTC	qwen/qwen3.6-35b-a3b	Impact: 55 Quick Win: 35.75 Staleness: 0 Complexity: 35 Confidence: 75 Support Request: 10	keep open	Enhancement to detect candid credentials in creds files and raise a user-friendly migration error, complementing existing env var checks.
2026-09-06 06:55 AM UTC	qwen3.6-35b-a3b-mtp-q6	Impact: 50 Quick Win: 35.0 Staleness: 5 Complexity: 30 Confidence: 80 Support Request: 10	keep open	Enhancement to detect candid credentials in creds files and raise a user-friendly migration error. Partially implemented (env var check exists), but creds file parsing is missing.

Update history

Date	Change
2026-09-08 06:41 PM UTC	updated
2026-09-04 12:29 PM UTC	created

Related work

Likely Fixed By: snapcraft#6288 (confidence 85%)
PR #6288 removed candid login support and added env var checks in account.py, but the creds file detection mentioned in this issue was not implemented.

Related issues

No related issues found above the similarity threshold.