code: public void login(AuthenticatedUser user) throws AuthenticationException
      {
          if (!user.isAnonymous() && !Auth.isExistingUser(user.getName()))
             throw new AuthenticationException(String.format("User %s doesn't exist - create it with CREATE USER query first",
                                                             user.getName()));
          this.user = user;
      }
docs: Attempts to login the given user.