$entityBody = file_get_contents('php://input');
$body = json_decode($entityBody,true);
foreach ($body as $value)
{
    $username    = $value['username'];
    $oldPassword = $value['oldPassword'];
    $newPassword = $value['newPassword'];
}

$con = new MongoDBClient;
if($con){
    $db = $con->users;
    // Select Collection
    $collection = $db->user;

$filter = array(['Username' => $username,
                     'Password' => $oldPassword
                     ]);

    $qry = new MongoDBDriverQuery($filter);

$rows = $collection->findOne($qry);

if($rows['Username']== $username && $rows['Password'] == $oldPassword)
    {
        $criteria = ['Username' => $rows['Username']];
        $newData = ['$set' => ['Password' => $newPassword]];

        $collection -> update($criteria,$newData);
        $changed = true;

         echo json_encode(array('status'=> '1','isChanged' => $changed));
    }
    else{

    $changed = false;
    echo json_encode(array('status'=> '2','isChanged' => $changed));
    }
    }
    else
    {
        die("Mongo DB not connected!");
    }