All friedolin-belonging data is kept on your phone or sent to the Friedolin. The connection this way is encrypted with SSL (HTTPS) for your security.
The data for the partys is sent to my server ofc, so it can manage the parties. It will send all the data you see there, your login name (e.g. xa00yaz), and your logged in (real life) name. Users will only be able to see your rl name, not the other one.
As long as you're nice to my party management server, I won't send the password for authentification, and you don't need to log in with another way besides the Friedolin. You'll be informed if I change that ofc :).
The project is open source ofc :D, so you can have a look yourself, what I do with your login and other data :3. See it on GitHub.