EDIT:
I just realised you asked for an option to place info in another text box ...
Within construct you ca easily stuff something in a global variable and use it later somewher else ...
As to data settting and retrieval elsewhere, outside of your game ..
I use php scripting for that
you need:web server,php and/or mysql database
Ajax post url with parameters (ie: username, pass, safety code, page request, etc)
That url is your PHP page which needs to use the variables from the $_POST['username'] which its receiving fromyour construct 2 application.
For a user system this should be checked in php versus the mysql table.
The php page should should echo some sort of result, I use the tokenat for that, ie:
<?php
....process constructs 2 ajax call and give results....
echo "success|you have logged in";
?>
in Construct fetch the php echo from the ajax call with AJAX.LastData.
I then do: if tokenat(AJAX.LastData, 0, "|") (check string before pipe sign) check if its "success"
If the user entered wrong info, you could have php echo "failed|incorrect pass";
and have it display the second bit after the pipe to relay info what was wrong :) (wrong pass)
Hope that makes it a bit more clear.