1) Create a file on your webserver (website) with this code (your site must run PHP, most do)

<?      
header('Location: http://applicationurl.customerhub.net/web_services/auto_login?email='.$contacts[0]['Email'].'&password='.$contacts[0]['Password']);
?>

You'll need to change "appname" in the code above to match your CustomerHub URL.

2) Let's assume your the URL that you put that code at is http://www.mysite.com/customerhub/login.php

3) Make a trackable link where the destination URL is http://www.mysite.com/customerhub/login.php

4) Click on "More Options" 

5) Select BOTH Email and Password as fields to be passed.  Hold down Control to select two items. Then save and you're done. (See attached screenshot)