html - cURL using php and json -

hey guys having trouble curl using php. have front-end on 1 server, middle on 1 server, , back-end on server. suppose communicate each other using curl. front-end person enters there username , password, there front-end uses curl send middle $_post fields username , password, after middle passes them along back-end checks within database , echo's whether credentials legit. reason keep getting "null" after tries login. should print "success" or "no". think problem json variable back-end echoing. not sure here code fragments. doing wrong?

front-end

<?php    // sends user name , password middle end , checks cookies  $username = $_post['username']; $password = $_post['password']; $url1= "https://web.njit.edu/~kc328/mid.php"; $cookie="cookie.txt";  $postdata = array("ucid" => $username, "pass" => $password);   //authenticate against our database $ch = curl_init();  //echo $ch; curl_setopt ($ch, curlopt_url, $url1); curl_setopt ($ch, curlopt_ssl_verifypeer, false); curl_setopt ($ch, curlopt_timeout, 60); curl_setopt ($ch, curlopt_followlocation, 0); curl_setopt ($ch, curlopt_returntransfer, 1); curl_setopt ($ch, curlopt_cookiejar, $cookie); curl_setopt ($ch, curlopt_referer, $url1); curl_setopt ($ch, curlopt_postfields, $postdata); curl_setopt ($ch, curlopt_post, 1); $result = curl_exec($ch);  curl_close($ch);     // $arr=json_decode($result, true);   $type = $arr['usertype'];  $username = $arr['username'];   //    $arr = var_dump(json_decode($result, true)); //     //    echo = $arr;   ?> 

middle

<?php  //$credentials= file_get_contents('php://input'); $credentials=array("username"=>$_post["ucid"], "password"=>$_post["pass"]);  $url1="https://web.njit.edu/~vm276/connect.php"; //$url1="https://www.njit.edu/cp/login.php"; $ch = curl_init(); curl_setopt ($ch, curlopt_url, $url1); curl_setopt ($ch, curlopt_ssl_verifypeer, false); curl_setopt ($ch, curlopt_timeout, 60); curl_setopt ($ch, curlopt_followlocation, 1); curl_setopt ($ch, curlopt_returntransfer, 1); curl_setopt ($ch, curlopt_cookiejar, $cookie); curl_setopt ($ch, curlopt_referer, $url1); curl_setopt ($ch, curlopt_postfields, $credentials); curl_setopt ($ch, curlopt_post, 1);  $result = curl_exec($ch); curl_close($ch); $json=json_decode($result); var_dump($json); echo $json->result;      ?> 

back-end

<?php //initialize variables connect db $dbuser = "xxxxx"; $dbpass = "xxxxx"; $host = "xxxxx"; $dbname = "vm276";  //database connection $connect = mysqli_connect($host,$dbuser,$dbpass,$dbname);  //connection doesnt work if (!$connect) {     //echo "error failed " . php_eol;     //echo "failed attempt again " . mysqli_connect_errno() . php_eol;     //echo "sorry, no go " . mysqli_connect_error() . php_eol;     exit; }  //connection work else {         //echo "connection success!!!";     //$user = "test1";     //$pass = "pass1";     $user = $_post['username'];     $pass = $_post['password'];     //$check = $_post['check'];     $sql = "select * users username = '$user' , password = '$pass'";      //check if user exists     $res = mysqli_query($connect,$sql);     $amt = $res->num_rows;      //sql record found         if ($amt == 1)     {         $json =array("result"=>"yes");     }      //sql record not found     else     {         $json = array("result"=>"no");     }      mysqli_close($connect);      echo json_encode($json); }  ?>