Payment Initiation - platform integration

Looking at the draft spec from Digital Bazaar for the CG and considering
both, our language in the charter, and also some of the comments from the
charter AC review I wondered what precedent there may be in defining how a
browser should process an API call that requires interaction with the
platform (host OS).

The best example I could find is in the Web Notifications PR published
earlier this month:
http://www.w3.org/TR/2015/PR-notifications-20150910/#displaying-notifications

I would like to get the groups' (both IG and CG) views on the parallels
here between the action "Displaying Notifications" from the Web
Notifications recommendation and a potential "Initiating Payments" section
we'd put in a recommendation from our WG.

The pertinent line from the Web Notifications rec is:
"Display notification on the device (*e.g. by making the appropriate
notification platform API call*)." - emphasis mine.

While I know not all platforms upon which browser's run today have mature
"payment APIs" in the same way that they have relativley mature
"notifications APIs" this open-ended approach seems appealing in that it
avoids the browser needing to become complex payment processing
applications.

Rather, the messages passed to the navigator.payments API in the browser
should simply be passed directly to the platform's payment API (following
any security or privacy scrutiny or permissions checks we define).

The timing seems right for us to work with the platform vendors (many of
whom are also browser vendors that have expressed interest in working on
this problem) to define a common vocabulary and logical messages for this
flow.


*Example:*
On a mobile platform I see this working similarly to the way Android
intents may function. The browser passes the payment initiatiation request
to the platform and the user is prompted with the app selection dialogue
they are accustomed to for selecting the app they want to use for that
action (the same way you select which app to use when sharing a photo for
example).

Thoughts?