enabling cors in codeigniter ( restserver by @chriskacerguis )

Try adding OPTIONS to the allowed methods.

header("Access-Control-Allow-Methods: GET, OPTIONS");
header("Access-Control-Allow-Headers: Content-Type, Content-Length, Accept-Encoding");

and return immediately when the request is method 'OPTIONS' once you have set the headers.

if ( "OPTIONS" === $_SERVER['REQUEST_METHOD'] ) {
    die();
}

See also this answer.

Angular sends a W3C CORS spec compliant preflight request that will check for the right allowed methods before actually attempting it.

Personally, I find the Mozilla Developer Network CORS page a bit easier to read on the matter to help understand the flow of CORS.

I've added the following constructor in my controller class

public function __construct($config = 'rest')
{
    header('Access-Control-Allow-Origin: *');
    header("Access-Control-Allow-Methods: GET, POST, OPTIONS, PUT, DELETE");
    parent::__construct();
}

If anyone else is facing the issue, enabling CORS in rest.php file of Codeigniter REST Controller worked for me. This is also clearly documented in comments here https://github.com/chriskacerguis/codeigniter-restserver/blob/master/application/config/rest.php

//Change this to TRUE
$config['check_cors'] = TRUE;

//No change here
$config['allowed_cors_headers'] = [
  'Origin',
  'X-Requested-With',
  'Content-Type',
  'Accept',
  'Access-Control-Request-Method',
  'Authorization',
];

//No change here
$config['allowed_cors_methods'] = [
  'GET',
  'POST',
  'OPTIONS',
  'PUT',
  'PATCH',
  'DELETE'
];

//Set to TRUE to enable Cross-Origin Resource Sharing (CORS) from any source domain
$config['allow_any_cors_domain'] = TRUE;


//Used if $config['check_cors'] is set to TRUE and $config['allow_any_cors_domain'] is set to FALSE. 
//Set all the allowable domains within the array
//e.g. $config['allowed_origins'] =['http://www.example.com','https://spa.example.com']

$config['allowed_cors_origins'] = [];