Form submission in JSON format via AJAX - php

Question

I'm trying to submit a HTML form to a server and it fails. I have several issues here.
I'm making a CORS request. It is a request by the client and I can't do anything about it.
( My app resides in localhost:3000/login.html & My server resides in http://localhost:3001/Login/auth )
The server in localhost:3001 accepts JSON requests and give back a JSON Responce.
(I have disabled the web-security in the browser to allow the CORS Requests)
So, I have created the HTML Form and tried to submit it with AJAX. Here you can see the code.
$(function(){
$("#loginform").submit(function(e){
e.preventDefault();
// var data = $("#loginform").serialize();
var data = {"username" : $("#username").val(),"password" : $("#password").val()};
alert(JSON.stringify(data));
$.ajax({
type: "POST",
url: "http://localhost:3001/Login/auth",
data: data,
contentType: "application/json",
crossDomain : true,
dataType: "json",
success: function(data) {
alert("success" + JSON.stringify(data));
},
error:function(data){
alert('error : '+JSON.stringify(data));
}
});
});
});
I have created the mock server in PHP (codeigniter). Here is the code for that.
public function auth(){
$input_data = json_decode(trim(file_get_contents('php://input')), true);
$debug_export = var_export(file_get_contents('php://input'), true);
file_put_contents('new.txt',$debug_export . PHP_EOL, FILE_APPEND);
$user = 'admin';
$pass = 'admin';
$token = '1';
foreach($input_data as $key=>$value) {
if ($key === 'username') {
$this_user = $value;
}
if ($key === 'password') {
$this_password = $value;
}
}
if(isset($this_user) && isset($this_password)){
if($this_password === $pass && $this_user === $user){
echo json_encode(array('token'=>$token));
}else{
echo json_encode(array('token'=>'null'));
}
}
return 0;
}
When I submit a form, I get a response like this.
....
<p>Severity: Warning</p>
<p>Message: Invalid argument supplied for foreach()</p>
<p>Filename: controllers/Login.php</p>
<p>Line Number: 77</p>
....
My 'new.txt' file has the log details as following.
''
'username=admin&password=admin'
I have really no idea what I'm doing wrong here. Can anyone help me out here?