login multi user

<?php

if(isset($_POST['act']))
{
ob_start();
    $select="<option>Pilih Tipe</option>";
    foreach($_POST as $nm=>$val)$$nm=$val;
/*
    asumsikan username=admin
    password=43211234
*/
    if($username=='admin' && $password=='43211234')
    {
        $loginOK=TRUE;
    }else{
        //tidak valid
        $alert="Periksa kembali User dan Password Anda";
    }

//=============BILA MEMILIH TIPE YANG TERSEDIA dan login OK
    if(intval($type)==0&&$loginOK==TRUE)
    {
//==============LIST YANG BISA DI AMBIL== BELUM MEMILIH TIPE
        $row=array(1=>'admin','kasir','moderator');
        $select="";
        foreach($row as $id=>$name)
        {
            $select.="<option value='{$id}'>{$name}</option>";
        }

    }elseif($loginOK==TRUE){
//============Memeriksa Apakah memilih Kasir (2) bukan yang lain
        if($type==2)
        {
/*
dalam praktek hanya cross check apakah akses yg dipilih memang dimiliki/ tidak
*/
            $loginOK=TRUE;
//========AlAMAT YANG AKAN DI TUJU
            $url="usercp";
/*
    proses input ke session
*/
            $_SESSION['username']=$username;
            $_SESSION['userpass']=md5($password);
            $alert="Selamat Datang ".$username;
        }else{
            $loginOK=FALSE;
            $alert="Periksa kembali Role Anda";
        }

    }

    $post=ob_get_contents();
    ob_end_clean();
    $a=array(
        'post'=>$post
    );

    if(isset($select))
    {
        $a['type']=$select;
    }

    if(isset($url))
    {
        $a['url']=$url;
    }

    if(isset($alert))
    {
        $a['alert']=$alert;
    }



$json= json_encode($a);
die($json);
}
?>
<script src='js/jquery.1.8.2.js'></script>
<script>
function checkLogin()
{
    var selectorform="form#login";
    var datax = $(selectorform).serialize();
    console.log('check login');
    var request = $.ajax({
          url: "?act=34",
          type: "POST",
          data: datax ,
          dataType: "json"
    });

    request.success(function(msg) {
       console.log('berhasil');
       if(msg.type)
       {
          $(".selType").empty();
          $(".selType").append(msg.type);

       }

       if(msg.alert)
       {

        $(".info").html(msg.alert);
        alert(msg.alert);
       }

       if(msg.url)
       {
        window.location =msg.url;
       }
    });

    request.fail(function(jqXHR, textStatus) {
      alert( "Request failed: " + textStatus );
    });
    return false;
}
</script>
<form id="login" class="block">
        <h3>LOGIN</h3>
        <p class="text-warning info">&nbsp;</p>
        <input type='hidden' name='act' value='login' />
        <dl>
            <dt>Username</dt>
            <dd><input name="username" type="text" placeholder="your username" value=""></dd>
            <dt>Password</dt>
            <dd><input name="password" type="password" value=""></dd>
            <dt>Type</dt>
            <dd><select name="type" class="selType"><option value="0">Pilih Type
            </option></select></dd>
            <dd><input name="submit" class="btn" type="button" value="Login" onclick="checkLogin();return false;"></dd>
        </dl>
</form>
<br/>username = admin
<br/>password = 43211234