Integration with external login

I'm building a website which was protected by SSO.
I plan to create a php file when SSO login callback, I will get the SSOID and user related info in http head. then auto login drupal or create a new user programatically.
Here's my code:

<?php

require 'includes/bootstrap.inc';
require 'modules/user/user.module';

function getSSOID(){
   .......
}

function getUserEmail(){
    .......
}

function createUser($username,$pwd,$email) {
  $edit = array(
    'name' => $username,
    'pass' => $pwd,
    'mail' => $email,
    'status' => 1,
    'language' => 'en',
    'init' => 'admin@drupal.com',
    'roles' => array(2 => 'authenticated user'),
  );
  user_save(NULL, $edit);
}


$ssoid = getSSOID();
$useremail = getUserEmail();
$user = user_load_by_name($ssoid);

if(!$user){
    // User doesn't exist
    createUser($ssoid,"",$useremail);
} 
else {
    // User exists
    drupal_session_regenerate();
}
//write a redirect code if necessary
$url="http://localhost:8080/drupal718/";
header("Location: $url");
?>

I'm new to drupal, I can not make this to work....anyone can help me....thanks in advance!