This feature is named 'Make this feed private' feature and can be found under Optional features.
You can use 'Send me summary e-mail' option to receive feed settings including your currently defined user name and password.
I must additionally say that if you make your feed private, typed in credentials will be sent each time over the network by HTTP protocol in plain text (pretty insecure). We plan to add HTTPS protocol support in the futute to make your feeds truly private and secure.
Other recent improvements include:
- 'Delivered by Feed43 service' tagline now appears less frequently depending on the content length of news items.
- Feed title and item title are automatically truncated to max. 150 symbols (some news readers don't like too long headings).