Convoy: Cross-Tenant Source IDOR Leaks Plaintext Message Broker Credentials

## Summary frain-dev/convoy (all versions up to and including v26.6.2, no patch available) lets any authenticated caller who is authorized on at least one project read ANY OTHER project's "Source" record by ID via GET /api/v1/projects/{projectID}/sources/{sourceID} -- regardless of whether that Source actually belongs to the project named in the URL. The response includes the Source's full PubSub broker configuration in plaintext (AMQP/Kafka/SQS/Google credentials), with no redaction. ## Details `Handler.GetSource` (api/handlers/source.go) resolves the caller's authorization against the {projectID} in the URL via retrieveProject(), then calls `sources.Service.FindSourceByID(ctx, project.UID, sourceID)` (internal/sources/impl.go). That function accepts a projectID parameter but never uses it: func (s *Service) FindSourceByID(ctx context.Context, projectID, id string) (*datastore.Source, error) { row, err := s.repo.FetchSourceByID(ctx, common.StringToPgText(id)) ... } The underlying SQL query (internal/sources/repo/queries.sql, `fetchSourceByID`) has no project_id predicate at all: SELECT ... FROM convoy.sources AS s LEFT JOIN convoy.source_verifiers sv ON s.source_verifier_id = sv.id WHERE s.id = $1 AND s.deleted_at IS NULL So the {projectID} in the URL only gates "is the caller authorized to view *a* project" -- it never re-validates that the fetched Source actually belongs to that project. `LoadSourcesPaged` (the list endpoint) does correctly scope by project; only the singl