This plugin solves an important problem for me: It allows non-premium users with Floodgate or Ely.by usernames to join an online-mode server.

However, it still has a few errors. For example, sometimes the database can become corrupted for unknown reasons. Another thing is that the commands don't respond correctly when players are being added to the whitelist, or the whitelist doesn't exist (the proxy doesn't have a whitelist enabled).