Store user session Corona SDK - php

Question

I am trying to build a social app using Lua(Corona SDK). What I want to do is save the user in a session when they login/register so they won't have to login whenever they close the app and open it again.
I am sort of confused because I don't really know much Lua but my code doesn't work. I am using PHP and MySQL as the backend and DB. I already save the user in a session in PHP but how do I show the session id to the front end and verify it so that I can automatically login in ?
local function networkListener( event )
if ( event.isError ) then
local alert = native.showAlert("Error Logging In", "Check your internet connection .", {"Try again" })
else if event.response == "success" then
-- put the code here to go to where the user needs to be -- after a successful registration
--username = userID
composer.setVariable( "username", username.text )
composer.gotoScene( "feed", { params = parametersToSend } )
composer.removeScene( "login" )
else -- put code here to notify the user of the problem, perhaps -- a native.alert() dialog that shows
--them the value of event.response -- and take them back to the registration screen to let them try
--again
local json = require("json") print( json.prettify( event ) )
local alert = native.showAlert( "Error Logging In", event.response , { "Try again" } )
end
end
end
local function userLogin(event)
if ( "ended" == event.phase ) then
if emptyFields() == true then
else
local parameters = {}
parameters.body = "Login=1&username=" .. username.text .. "&pw=" .. pw.text
local URL = "http://192.168.1.37/hashmobile/process2.php"
network.request(URL, "POST", networkListener, parameters)
local headers = {}
headers["Content-Type"] = "application/x-www-form-urlencoded"
headers["Accept-Language"] = "en-US"
parameters.headers = headers
end
end
end
process2.php:
$sql = "SELECT pw FROM users WHERE username = ?";
$stmt = mysqli_prepare($con, $sql);
$stmt->bind_param('s', $username);
$stmt->execute();
$stmt->bind_result($hashed_pwd); // Binds variables to a prepared statement for result storage
$stmt->fetch(); // Fetch results from a prepared statement into the bound variables
if (password_verify($pw, $hashed_pwd)) {
//session_id($_POST['user_session_id']); //starts session with given session id
// password verified
$_SESSION["user_session_id"] = $username;
echo "success";
//echo $_SESSION["user_session_id"];
//header('Location: profile.php');
//die();
} else {
//echo 'Incorrect username or Password.';
die('Incorrect username or Password.');
}
That is how I login to my app. Any help ?