Api.php

<?php defined('BASEPATH') OR exit('No direct script access allowed');

Class Api extends CI_Controller
{
    public function __construct()
    {
        parent::__construct();
        $this->load->model('api_model','api');
        
        //I stumbled into issues when testing on my local development server
        // adding this simple piece of code helps me send a request from a frontend on a different server
        // to this api on a different server
        // I was making a request from Angular login from localhost:4200 to PHP webserver localhost:8090
        header("Access-Control-Allow-Origin: *");
        header("Access-Control-Allow-Methods: GET, OPTIONS");
        header("Access-Control-Allow-Headers: Content-Type, Content-Length, Accept-Encoding");  
        if ( "OPTIONS" === $_SERVER['REQUEST_METHOD'] ) {
            die();
        }
    }

    public function login()
    {
        //Do form validation with codeigniter
        $this->form_validation->set_rules('username', 'Username', 'required');
        $this->form_validation->set_rules('password', 'Password', 'required');
        if($this->form_validation->run() == FALSE)
        {
            //If form validation failes store error array
            $output['errors'] = $this->form_validation->error_array();
        } else {
            // If everything is Okay. Capture username and password post data
            $username = $this->input->post('username');
            $password = $this->input->post('password');
            
            //Get userdata from the Api_model
            $userdata = $this->api->authenticate($username, $password);
            
            //Get the ID & Token
            $id = $userdata['user_id'];
            $token = $userdata['token'];
            
            //Check if id exists
            if($id != false) {
                
                //If token does not exist the we generate one using PHP-JWT library
                if(! isset($token)) {
                    $key = base64_encode('add some randome key here');
                    $payload = array(
                        "iss"     => "Add website address here",
                        "iat"     => time(),
                        "exp"     => time() + (3600 * 24 * 15),
                        "context" => [
                        "user" => [
                                "username" => $username,
                                "user_id"    => $id
                            ]
                        ]
                    );

                    $jwt = JWT::encode($payload, $key);
                    
                   //Output the token and user_id

                    $output['errors'] = "";
                    $output['token'] = $jwt;
                    $output['user_id'] = $id;
                } else {
                    
                    //Output the token and user_id
                    $output['errors'] = "";
                    $output['token'] = $token;  
                    $output['user_id'] = $id; 
                }

            } else {
                $output['errors'] = 'User does not exist';
            }

        }

        echo json_encode($output);
    }
}