fix(api)!: retrieve on unexisting ressource should not return an error

By returning errors, it drastically increased the error rate in OTEL spans/Jaeger monitoring which is semantically invalid: there was no service failure/downgrade, only a check to know if an API object existed or not.

api/v1/challenge/retrieve.go

@@ -76,6 +76,10 @@ func (store *Store) RetrieveChallenge(ctx context.Context, req *RetrieveChalleng
 	// 4. Fetch challenge info
 	fschall, err := fs.LoadChallenge(req.Id)
 	if err != nil {
+		// If challenge not found, is not an error
+		if _, ok := err.(*errs.ErrChallengeExist); ok {
+			return nil, nil
+		}
 		if err, ok := err.(*errs.ErrInternal); ok {
 			logger.Error(ctx, "loading challenge",
 				zap.Error(err),

api/v1/instance/retrieve.go

@@ -109,6 +109,10 @@ func (man *Manager) RetrieveInstance(ctx context.Context, req *RetrieveInstanceR
 	// 6. If instance does not exist, return error
 	fsist, err := fs.LoadInstance(req.ChallengeId, req.SourceId)
 	if err != nil {
+		// If instance not found, is not an error
+		if _, ok := err.(*errs.ErrInstanceExist); ok {
+			return nil, nil
+		}
 		if err, ok := err.(*errs.ErrInternal); ok {
 			logger.Error(ctx, "loading challenge instance",
 				zap.Error(err),