Using getAuthPassword() with another Model instead of User Model?

I am facing issue, I want to use different field name for password. let us say in users table, when I use this code with User model it works perfectly

/**
 * Override required, otherwise existing Authentication system will not match credentials
 * @return mixed
 */
public function getAuthPassword()
{
    return $this->userPassword;
}

but when I use it with another Model let us say Customer model with same table structure , it doesnt work??!!! does anyone have idea about this issue

Thanks in advance.

via Chebli Mohamed