Steven, I think the help article you provided is for Marketo users to access Marketo, not for external customers to just access elements of their lead record. Hitoshi's suggestion would allow customers to see read-only data related to their account. You could use a form on that same page to allow them to update fields in their record but it would be dependent on the presence of the _mkto_trk cookie to pre-populate the form fields with the current data. Is there another help article with more information about this - I couldn't find one?