json validation in codeigniter

How to validate json data or json nested array in codeigniter

For example we have two fields email and password to validate and sending request from postman as shown below:
request method: post
{
    "email":"sachinsharma.one@gmail.com",
    "password":"12345"
}

In controller

public function login_post()
{
header('Content-type: application/json');

                $request = json_decode(file_get_contents('php://input'),true);

$this->form_validation->set_data($request); /// for setting data

$this->form_validation->set_rules('email','Email', 'required|valid_email');
$this->form_validation->set_rules('password','PASSWORD', 'required|min_length[4]|max_length[20]');

if($this->form_validation->run()==false)
{
echo validation_errors();
}
else
{
// your code..............
}
}

In this way you can validate json data or even big json data