Login with email on codeigniter from database

Question

i'm building an Api, i need to login in a codeigniter-restserver project with an email + password stored on my mysql database.

this what i tried so far:

in my REST_Controller i changed the _check_login function with this:

$this->load->model('Model_logiin');
$valid_logins = $this->Model_logiin->get_by(array('student_id'=>$username));

please take a look at the complete code here : https://github.com/chriskacerguis/codeigniter-restserver my

Model Model_logiin is this:

class Model_logiin extends MY_Model{

protected $_table = 'students';
protected $primary_key = 'email_adress';
protected $return_type = 'array';

protected $after_get = array('remove_sensetive_data');   //specified in MY_Model class

protected function remove_sensetive_data($student){

    unset($student['ip_adress']);
    unset($student['student_id']);
    ...

    return $student;
}
}

The Problem: in the login stage.. if i type anything i can login

** if you need more info please let me know

** if the best approach for an api to not login with email just API-Key also please let me know

** i'm new to codeigniter.