[fprint] fprintd single sign on limitation

[Igor Filatov]

I think Dave means that the scanner would capture the print when the device
is powered on. Not as instructed by a userspace driver, but as a "hardware
feature" of the button/sensor itself. It would store a single image until
asked by libfrint to perform a scan, at which point it would just submit
the image it has. libfprint doesn't need to know. It only needs to match
the print not aginst the library of a chosen user, but of all users and
return a pair of (ok, user_id).


On Fri, 7 Dec 2018, 14:36 Bastien Nocera, <hadess at hadess.net> wrote:

> Hello Dave,
>
> On Wed, 2018-11-14 at 10:13 +0800, Dave.Wang wrote:
> > Dear Bastien,
> >
> > Thanks for your quick reply!
> >
> > Feeling sorry for not indicating clearly about our definition of SSO
> > In our definition of SSO,
>
> What I was saying is that you shouldn't be using "SSO" as a name, it's
> already something that exists, and that is completely different from
> what you're describing below:
> https://en.wikipedia.org/wiki/Single_sign-on
>
> > 1. Our fingerprint sensor is located on power button of notebook
> > 2. Driver would inform device to pre-capture image while someone
> > touch the power button.
> > 3. In login phase, user wouldn't have to identify finger if the pre-
> > capture image is existed
> > 4. Driver would submit that pre-capture image to algorithm if the
> > pre-capture image is existed, and then login to its corresponding
> > account.
>
> I don't understand at which point the user-space driver would be able
> to tell the power button's IC to capture the image, or where that image
> would end up being stored. Would the driver tell that to the power
> button's IC/fingerprint reader before the machine gets turned off?
>
> > In your opinion, is it possible to implement SSO in libfprint?
> > Thank you very much for your time and suggestion!
>
> There are multiple steps to that, and the first one would be to extend
> fp_driver internally to allow setting that "remember fingerprint on
> next boot", as well as providing a way to extract the "remembered"
> fingerprint.
>
> After that, integration work into the OS can start. I think we would be
> taking cues from the smartcard integration done in gnome-settings-
> daemon[1] and integrate it in fprintd.
>
> Access to hardware and specs would be much appreciated if you want more
> help doing this integration. It's pretty difficult designing for a use
> case in a vacuum. I'd recommend looking into this once the work has
> been done in libfprint to support the hardware features.
>
> Cheers
>
> [1]:
> https://gitlab.gnome.org/GNOME/gnome-settings-daemon/tree/master/plugins/smartcard
>
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