Importing users

Hello,

I have imported my old users into CMSUsers. I have added the following loader attribute:

public override void Init()
    {
        SecurityEvents.Authenticate.Execute += OnAuthenticateExecute;
    }

    private void OnAuthenticateExecute(object sender, AuthenticationEventArgs e)
    {
        try
        {
            UserInfo objUserInfo = UserInfoProvider.GetUserInfo(e.UserName);
            if (objUserInfo == null)
                return; // user doesn't exist

            bool blnIsImportedUser = objUserInfo.GetValue<bool>("IsImportedUser", false); // is this an imported user?
            if (blnIsImportedUser)
            {
                string strEncryptedPassword = objUserInfo.GetValue<string>("ImportedEncryptedPassword", string.Empty); // get the imported password
                string strPasswordSalt = objUserInfo.GetValue<string>("ImportedPasswordSalt", string.Empty); // get the imported salt

                if (string.IsNullOrWhiteSpace(strEncryptedPassword) || string.IsNullOrWhiteSpace(strPasswordSalt))
                    return; // pass and/or salt not set

                ImportedAuthentication objImportedAuth = new ImportedAuthentication(); // use old authentication
                if (strEncryptedPassword.Equals(objImportedAuth.EncodePassword(e.Password, strPasswordSalt))) // is password correct?
                {
                    UserInfoProvider.SetPassword(objUserInfo, e.Password); // set the kentico password to the same as the user enty
                    objUserInfo.SetValue("IsImportedUser", false); // remove old user flag
                    objUserInfo.Update(); // save to kentico
                }
            }
        }
        catch (Exception ex)
        {
            ErrorHandler.HandleError(ex);
        }
    }

When an imported user attempts to log in, the code acts as expected. The kentico password is set and the flag is unset. However the authentication fails. On the next attempt, the authentication is successful. My guess is the authentication has already failed before it gets to my code. Is there a way of changing the password before kentico authenticates the user?

Thanks