<?php
// Read request parameters
$username= $_REQUEST["username"];
$password = $_REQUEST["password"];
// Store values in an array
$returnValue = array("username"=>$username, "password"=>$password);
// Send back request in JSON format
echo json_encode($returnValue);
?>

func getPHPJson() {

        let urlPath: String = "LINK_TO_PHP_FILE?username=(user)&password=(pass)"
        let url: NSURL = NSURL(string: urlPath)!
        let request1: NSMutableURLRequest = NSMutableURLRequest(URL: url)

        request1.HTTPMethod = "GET"
        let queue:NSOperationQueue = NSOperationQueue()

        NSURLConnection.sendAsynchronousRequest(request1, queue: queue, completionHandler:{ (response: NSURLResponse?, data: NSData?, error: NSError?) -> Void in

            do {
                if let jsonResult = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as? NSDictionary {
                    print(jsonResult)
                    //print(jsonResult["isUser"] as! Bool)
                    let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
                    print("raw response: (responseString!)")
                }
            } catch let error as NSError {
                print(error.localizedDescription)
                print("error")
                let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
                print("raw response: (responseString)")
            }
          })
    }
}

{
    password = iosappusettest1;
    username = iosappusettest;
}
raw response: {"username":"iosappusettest","password":"iosappusettest1"}

function authentication ($user, $pass){
  global $wp, $wp_rewrite, $wp_the_query, $wp_query;

  if(empty($user) || empty($pass)){
    return 0;
  } else {
    require_once('../wp-blog-header.php');
    $status = 0;
    $auth = wp_authenticate($user, $pass );
    if( is_wp_error($auth) ) {
      $status = 0;
    } else {
      $status = 1;
    }
    return $status;
  }
}