So this still works, just to be clear.
Your openHAB instance has a REST interface that is available through myopenhab using HTTP Basic auth (and your myopenhab username password) so you could have something update an item externally , for example using curl (command line http client) i can trigger a switch to “ON” like:
curl -u username:password -H "Content-Type: text/plain" -X POST -d "ON" https://myopenhab.org/rest/items/TestSwitch
Some systems may also use this format for auth, as long as they can send a POST command to a URL:
https://username:password@myopenhab.org/rest/items/TestSwitch
Just be careful exposing your system like this.
Does that help?