Client_1 wants to move right
Server broadcasts that
Clients simulating Client_1's movement
Client_1 sends it's coordinates to the server (every 100ms)
Server validates coordinates based on client's last position and last update (which is stored on the server)
Server corrects Client_1's coordinates on every client

var now = Date.now();
var clientX = ...x position sent by client...
var clientY = ...y position sent by client...
var timeDiff = Math.ceil((now - player.lastPositionUpdate)/5)*5;
var timeDiff = timeDiff > 1000 ? 1000 : timeDiff;
var pixelPer100 = player.speed/10;
var maximumPixelDiff = (pixelPer100/100) * timeDiff;
player.lastPositionUpdate = now;

if (clientX > player.position.x){
    var diff = clientX - player.position.x;
    newX = player.position.x + (diff > maximumPixelDiff ? pixelPer100 : diff);
}
..and more

update: function(){
    player.body.velocity.x = player.speed;
    tick++;
    if (tick == 6){
        tick = 0;
        sendPositionToServer();
    }
}