User.php

// models/User.php

/**
* Check if the user used the domain prefix
* to login. If they did pass param through
* unchanged. If they didn't, prepend it and
* return it.
* @param string $username
* @return string
*/
protected function checkUsername(string $username)
{
    if (!substr($username, 0, 4) == "DOM\\")
    {
        $username = "DOM\\" . $username
    }
}