Does not work with non-standard authentication (e.g. LDAP) on Sugar

This interfaces with leadCapture.php, or (in newer versions of Sugar) the leadCapture entryPoint (modules/Leads/Capture.php). Unfortunately, that uses the user_authenticate function from modules/Users/User.php, which does a bald comparison with Sugar's users table. Which means, if you are using any other form of authentication, it won't work, because the entry won't be in the table.

Not a fault in sugarForm, as such, but a limitation in sugar's leadCapture facility.