Include payment handler information in response

[ianbjacobs]

We have heard use cases for merchants having information about the user's selected payment handler for a transaction, including:

• Being able to debug issues
• Security / Trust in some payment handlers

This is most useful for standardized payment methods but may also be useful for URI-identified payment methods that allow for multiple payment handlers.

The original payment handler issue is 217:
w3c/payment-handler#217

I am not proposing this for a v1 feature. However, when we start to consider the issue we can return to a proposal to return two bits of information in the PR API response:

handlerType: {'built-in', 'web', 'native')
handlerID: {null, <origin>, <platform-specific> }

Ian

[rsolomakhin]

Can we reuse the field names "platform" and "id" from ExternalApplicationResource dictionary? Chrome already parses it in web app manifests to authenticate native Android payment apps.

Android:

"handler": {
  "platform": "play",
  "id": "com.example.app1",
}

Web:

"handler": {
  "platform": "web",
  "id": "https://app1.example.com",
}

Built-in:

"handler": {
  "platform": "built-in",
  "id": null,
}