<amp-viewer-assistance> extension

[dreamofabear]

Motivation

AMP has two properties that make it an attractive solution for distributed commerce:

1. It's safe to embed an AMP page in another property.
2. There is a clear privacy boundary between the AMP page and the AMP viewer.

The proposed amp-viewer-assistance extension standardizes certain messaging between AMP pages and AMP viewers so that developers can optimize their transaction flows for the platforms in which those flows will be embedded. For example:

• If users of a platform are signed in, then the platform already knows the user's name, contacts, payment method, calendar, etc.
• A merchant's AMP page can ask the platform's AMP viewer for that personal information. The viewer takes care of prompting the user to share that information.
• This streamlines the transaction flow because the user doesn't have to re-type information. They can simply reuse information they've previously provided to the platform.
• The same AMP page can work on other platforms that have their own viewer implementations.

Requirements

• Support viewer facilitation of transactional user flows for identity, form input and order completion.
• Support platform-agnostic configurability.

Proposed design

Platform configuration

Different platforms may require different metadata for these platform-optimized AMP pages. That is done using the following <script> tag:

<script id="amp-viewer-assistance" type="application/json">
{
  "platformA": {
    "foo": 123,
    "bar": 456,
  },
  "platformB": {
    ...
  }
}
</script>

The amp-viewer-assistance extension sends this JSON object to the viewer on page load.

Identity facilitation

In order to help users quickly authenticate and/or create an account with the AMP page, the amp-viewer-assistance extension will support identity flows.

The AMP page can prompt the user to sign in by calling the amp-viewer-assistance.signIn action. This will prompt the viewer to show an SSO UI (e.g. a dialog) and, if the user completes the sign in, a signedIn event will be triggered on the amp-viewer-assistance script tag.

If the user comes back to an AMP page from that same project at a later time, the user will be automatically logged in. The AMP page can access the identity token through the IDENTITY_TOKEN URL substitution variable.

Form input assistance

Autofill is another useful feature of platform-optimized AMP pages. The amp-viewer-assistance extension facilitates this by watching for events on the form fields and sending messages to the viewer, so that the viewer can suggest values for that field.

Order completion trigger

If a user wants to make a purchase in an AMP page, it can send the hosting platform information about that order by triggering the amp-viewer-assistance.actionCompleted(…) action.

[ampprojectbot]

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[dreamofabear]

This extension was added in #20725.