Re: [w3c/wcag21] Security of autofill (#590)

Don't confuse "autocomplete" (of a single field) with "autofill" (of
multiple fields in a form). I have not seen any implementations of
"autocomplete" that will automatically fill in single fields without
interaction, or fill in hidden fields. This feature has been around a lot
longer than 5 years; 20 maybe, 15 for sure. Adding autocomplete hints
shouldn't be harmful in this use, and by giving browsers hints it should
help users get more consistently useful data.

Password managers are an old form of "autofill" and in some implementations
will fill in hidden fields or fill without user interaction. This is
dangerous, but autocomplete hints won't make the problem worse.

More recently browsers started supporting a more explicitly acknowledged
form "autofill" that do take advantage of the autocomplete hints. I haven't
yet seen any that will fill forms without user interaction, but several
will go ahead and fill hidden fields if the user chooses to fill the form.
This is the source of the privacy worries you mention. Current autofill
implementations seem to be based around name-and-address type information
but it wouldn't be hard to imagine them expanding to incorporate data for
more of the standardized HTML5 autocomplete hints in the future.

The problematic user-interaction exists and needs to be mitigated whether
you recommend the use of the autocomplete attributes or not.

-Dan Veditz