Return a value from a PHP page after login

MIT App Inventor Help
1

I am creating a login page for app inventor application.
It is working fine but I need to bring back an ID to use it in the application.
What is the best way for doing that?
Partial code below:

$Email = mysqli_real_escape_string($dbc, $_GET['Email']);
$Pass = mysqli_real_escape_string($dbc, $_GET['Pass']);

$query = "SELECT * FROM Student WHERE Email = '". $Email . "' AND Pass = '" . $Pass . "'";
$result = mysqli_query($dbc, $query) or trigger_error("Query MySQL Error: " . mysqli_error($dbc));

if (mysqli_num_rows($result) > 0) {
echo "OK";
}
else {
echo "Invalid email/password!";
}
mysqli_close($dbc);

2

what about change
echo "OK";
to
echo $Email;
?