public override bool ValidateUser(string username, string password)
        {
            var passwordHash = new PasswordManager().EncodePassword(password, passwordFormat, machineKeySection.ValidationKey);

            var user = GetUser(username, false) as CouchDbMembershipUser;

            if (user == null) return false;

            return passwordHash == user.PasswordHash;
        }
        public override bool ChangePassword(string username, string oldPassword, string newPassword)
        {
            if(!ValidateUser(username, oldPassword)) return false;

            var newPasswordHash = new PasswordManager().EncodePassword(newPassword, MembershipPasswordFormat.Hashed, machineKeySection.ValidationKey);

            var user = GetUser(username, false) as CouchDbMembershipUser;
            
            user.PasswordHash = newPasswordHash;

            SaveUser(user);

            return true;
            
        }