Why the coturn server returning 401: Unauthorized

i have installed a Coturn server on ubunto 16 currently i'm checking it with

function checkTURNServer(turnConfig, timeout){ 

  return new Promise(function(resolve, reject){

    setTimeout(function(){
        if(promiseResolved) return;
        resolve(false);
        promiseResolved = true;
    }, timeout || 5000);

    var promiseResolved = false
      , myPeerConnection = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection   //compatibility for firefox and chrome
      , pc = new myPeerConnection({iceServers:[turnConfig]})
      , noop = function(){};
    pc.createDataChannel("");    //create a bogus data channel
    pc.createOffer(function(sdp){
      if(sdp.sdp.indexOf('typ relay') > -1){ // sometimes sdp contains the ice candidates...
        promiseResolved = true;
        resolve(true);
      }
      pc.setLocalDescription(sdp, noop, noop);
    }, noop);    // create offer and set local description
    pc.onicecandidate = function(ice){  //listen for candidate events
      if(promiseResolved || !ice || !ice.candidate || !ice.candidate.candidate || !(ice.candidate.candidate.indexOf('typ relay')>-1))  return;
      promiseResolved = true;
      resolve(true);
    };
  });   
}

const USERNAME="user"
const PASSWORD="password"
const PORT=3478
const IP="my_Coturn_server_ip" // you will have to change this

console.log('TURN server reachable on TCP?', await checkTURNServer( {
    url: `turn:${IP}:${PORT}?transport=tcp`,
    username: USERNAME,
    credential: PASSWORD,
}))

console.log('TURN server reachable on UDP?', await checkTURNServer( {
    url: `turn:${IP}:${PORT}?transport=udp`,
    username: USERNAME,
    credential: PASSWORD,
}))

every time i try to check i get this in the server

14: session 001000000000000001: realm user <>: incoming packet BINDING process ed, success 14: session 001000000000000001: realm user <>: incoming packet message process ed, error 401: Unauthorized 14: IPv4. Local relay addr: my_Coturn_server_ip:57906 14: session 001000000000000001: new, realm=, username=, lifetime=600 14: session 001000000000000001: realm user : incoming packet ALLOCATE pr ocessed, success 24: session 000000000000000001: realm user : incoming packet BINDING pro cessed, success

why it is returning 401 ? how i can open the server to public without authentication ?