Offer a simpler API for interaction URLs

[dlongley]

Given the evolution of CHAPI and the credential space, we could probably offer a drastically simplified API for issuer/verifier coordinator websites (relying parties) to call now. For example:

// this can either resolve (to an empty object or undefined at the moment)
// or it can reject with an `AbortError` because the user canceled from the UI
// or the caller (coordinator) aborted via `signal`
await navigator.chapi.interact({interactionUrl, signal});

Optional suggestions for credential handlers (e.g., digital wallets) could still be provided:

await navigator.chapi.interact({
  interactionUrl, signal,
  recommendedHandlerOrigins: [...]
});

The above entry point would then, for now, translate into a credentialrequest event to keep compatibility with existing use of the older API. If we need to translate into credentialstore as well, we can add another parameter for the caller to signal whether they are offering any credentials or just requesting them, e.g.:

// `type: 'store'` | `type: 'request'` to be bikeshed
await navigator.chapi.interact({
  interactionUrl, signal,
  recommendedHandlerOrigins: [...], type: 'store'
});

[dlongley]

In addition to the above, we should also offer a clear export from the polyfill (and documentation) that allows a caller to make a call without having to call loadOnce(). There are some considerations around things that must be added to a page and so on that might make this a performance challenge for first-time calls.

[ottonomy]

+1 to including both get and store functionality in this API, as interaction URls can do both. Eventually interact could be a real third method alongside these two primaries.

It would be nice to avoid navigator entirely to avoid getting constantly clobbered by password manager extensions and 🌟 exciting 🌟 new browser security restrictions.

[dlongley]

+1 to a pattern (somewhat) like this:

// noting it's more like a ponyfill at this point...
import {newLoadOnce} from 'credential-handler-polyfill';
globalThis.chapi = await newLoadOnce({...});

To allow users to attach the API wherever they'd like.