[paymentrequest] Support for "enrollment" use of API (#43)

Hi all,

Here is a use case that should be supported:

 * Service asks user at enrollment to register payment details for future use
 * API is used to retrieve those details, but no payment should actually take place.

Some payment apps might support this (e.g., raw credit card information) while others might not
(e.g., those that return 1-time tokens). 

What (if anything) does the API need to say to help readers recognize that it supports this 
enrollment use case? 

For example, suppose the preferred way to use the API for enrollment to specify amount=0.
The spec should say something to that effect and, for example, ensure that the definition of
amount supports that value.

Or, there might be other ways the API could support the enrollment use case. I look forward to
your thoughts.

Ian

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Reply to this email directly or view it on GitHub:
https://github.com/WICG/paymentrequest/issues/43