Is your suggestion for improvement related to a problem? Please describe.
Currently, the proxy configuration in Options -> Preferences -> Network requires the password being saved if the proxy needs an authentication.
As indicated by the warning message, the password is not protected, which raise a security concern.

Describe the solution you'd like
Do not impose to enter the password in the Preferences' field.
If the password is not saved, JabRef should prompt for it when using the proxy connection for the first time, and keep it in memory only for the current session.
Not a perfect solution, but an improvement.